My Enduring deck originally started life as a Reaper King/Scarecrow deck. That let all my creatures be Vindicates. I shifted more and more towards pure enchants when I realized how often my general and all the scarecrows were getting blown off the table by board clears, or worse, locked up by things like Path to Exile, Faith's Fetters and Arrest. Eventually I came to the conclusion that rushing to the EI lockdown was going to work better than struggling to keep any creatures in play, and that if all my creatures were doing was a single triggered effect before dying, I was probably better off investing in more enchants, which are harder to remove and can usually trigger a few times before someone manages to hate them. The scarecrows spun off into their own deck, filled with stuff to let them survive in EDH, but that required devoting a whole deck to it, and is a story for a different post.
That said, if you like how the creatures are working out for you, I can suggest the following for cheating them into play post epic, as possible alternatives to Oath:
Defense of the Heart - By far the easiest to trigger in EDH, especially if Dovescape is out, too. Wheel can cycle this back in and that's 2 or more creatures every turn.
Lurking Predators - Best in multiplayer, where several people might be casting each turn, and acts like a pseudo-Top, fixing your top deck to an extent.
Hibernation's End - Feed this with the output from Braid of Fire. You can let it reset every so often by not paying and letting Wheel of Sun and Moon recycle it.
Aether Vial - Another artifact that works out of hand, though it's best if there's a lot of similar costed creatures in your deck.
As far as creatures that might be interesting, due to their game changing effects, I'd probably try to favor board clearing effects, as your enchants already have the potential to seriously hinder almost any sort of control/combo based decks.
Reiver Demon - Board clear on a stick and a huge beater.
Malfegor - Post epic you'll have a big hand, which can force a lot of sacrifice on an opponent, and sacrifice is by far the best form of removal if you can get it.
Stalking Vengeance - Makes removal and board clears into damage to your opponents.
I've been working towards a similar sort of deck. The biggest difference is that I went with planeswalkers in place of creatures, figuring that having extra actions every turn once epic was more valuable than removable creature beats. I've also got Eternal Dominion as a backup to Enduring Ideal, if playing out of my opponent's deck would be more beneficial than using my enchantments (mostly if they've got recurrable enchantment hate that I can't easily remove) as well as ways to get them both out under ideal circumstances.
Early game, I feel I need significant card draw/advantage, until I can get my epics into hand and have enough mana to cast.
Maelstorm Nexus - Ideal usage for this is to use tutors (Vess/Mystical) to get Enduring Ideal on the top of the deck and then cast Eternal Dominion out of hand so they both are on the stack and can resolve. That gives me my one of my opponent's best cards plus one of my best enchants every turn. Huge card advantage. But even before that, cascading into other lockdown enchants or utility artifacts for free never hurts.
Sylvan Library - As good as Sensei's Divining Top for setting up combos with Maelstorm Nexus but also a source of general card draw. Due to the replacement effect this works very well with Parallel Thoughts and Mangara's Tome, as well as the "Words of" series of enchants. If you replace the draws, and have no cards that were drawn from library to put back, you don't have to pay the 4 life. Once you've gone epic, use this to help prevent drawing non-castable enchants into hand.
Mind's Eye - Artifact, not enchantment, but huge card draw in multiplayer games, especially versus draw-heavy control decks.
Rhystic Study - Again, huge potential card draw in multiplayer
Parallel Thoughts - I use this to load up my 'win' cards if possible. Eternal Dominion, Maelstorm Nexus, and tutors are my usual choices if I get this early. Then I play into the Cascade -> Enduring Ideal combo I mention above.
Mangara's Tome - Artifact version of Parallel Thoughts. If I get both out at once, I'll load one up with lands, in order to guarantee mana when I need it.
Night Dealings - Repeatable tutoring. Can be a little slow to get going, but with multiplayer bleeds/drains, it can spool up fast.
A quick note on the "Words of" series: Once you're epic, any of your previous card draw enhancement is mostly useless to you. These enchants turn that draw potential into extra "spells" each turn. Individually, a single draw replacement isn't that great, but if you've got three or four sources of extra card draw all going, you can get a lot of mileage out of these. If you're playing all those global draw punishing cards, these get even better, as they replace the draw and thus do not trigger damage for you.
For bleed effects, you're running pretty similar to what I do. Here's a few possibilities I've considered for my deck that you don't have. I don't run all of these at the moment, but I'm usually fiddling with a few of them, trying to find which combo works best.
Malignant Growth - This combos very well with Underworld Dreams, Spiteful Visions, Megrim and/or Bloodchief's Ascension for damage and Memory Erosion and Forced Fruition for mill/decking.
Antagonism - Punishes control and castle/turtle decks.
Nihilistic Glee - Allows you to discard useless cards in hand once epic for a bleed effect, great for getting enchantments back into the library via Wheel of Sun and Moon.
Repercussion - Makes Pestilience/Pyrohemia and Dovescape all the more vile.
Sanguine Bond - Bloodchief, Subversion, Nihilistic Glee, Polluted Bonds, Words of Worship, Honden of Cleansing Fire, Ajani Goldmane, Ajani Vengant, Sorin Markov, and Sun Droplet all can provide life gain in my deck. This turns those into more damage.
As part of my lockdown enchantments, I run a few land destruction and disruption enchants. These are primarily aimed at making counterspelling anything I play a serious drawback.
Defense Grid - Artifact, but makes counterspelling require lots of mana. Often my first Tezzert target if he comes out.
Price of Glory - Punish playing out of turn, combo with Defense Grid to truly make counterspelling hideous.
Choke - Another huge disruptor of control decks, especially MUC
Bloodmoon - Combined with Choke can completely destroy any MUC deck and seriously disrupt most others. And once you've gone epic, red mana is fine for almost all your upkeep/activated abilities.
Burning Sands - Since I run no creatures on my side this rarely can affect me, but destruction and board clears now also kill my opponents' lands.
For pure lockdown I have a few possible suggestions:
Humility - Amazing in a creature-light deck. Nearly equivalent to a global Faith's Fetters/Arrest and turns Pestilence/Pyhrohemia into repeatable board clears.
No Mercy - Shuts down aggro/token/weenie decks, especially comboed with Humility.
Spreading Plague - Keeps the number of creatures down to almost none. Dropping Child of Alara on the board with this will clear everything else, and then any subsequent creatures will kill it, triggering another board clear.
Rule of Law - More disruption for weenie/aggro and many control decks that rely on drawing and playing lots of cheap cards.
Necrogenesis - Normally I avoid token generators, but this is repeatable graveyard hate to lockdown recursion/reanimation oriented decks that happens to also make chump blockers. Good deal.
Decree of Silence - Automatic countering. Often times may be wasted on trivial spells, but in the worst case, let Wheel of Sun and Moon cycle it back into your deck and bring it out again next turn. Eventually you'll be stopping things that matter.
Aura Shards - I've taken this out of my deck, as I have so few ways to even make creature tokens, but if you run with more creatures/generators, this can wipe out opponent's artifacts/enchantments very quickly.
On the pure utility front:
Mirari's Wake - Extra mana in a 5 color deck never hurts, especially pre-epic.
Prismatic Omen - Makes any 5 color deck a lot more palatable, and makes utility lands much less of a drawback.
Braid of Fire - With the lack of mana burn, this never hurts, and with Paradox Haze, can turn into disgusting amounts of spare mana to pump into enchants or pay cumulative upkeeps with. Malignant Growth is a primary target for this mana, as is a Gemstone Array to turn it into other colors and store it for other phases.
Sterling Grove - Better than Greater Auramancy, IMO, as it can sac to search out an answer, if your opponent is not running significant enchantment hate and the shroud effect isn't needed.
Spirit of Resistance - I like this over Solitary Confinement in a 5 color deck, though I can see the usefulness of both.
Doubling Season - Amazing in any deck with planeswalkers. Lets most of them trigger their third ability immediately. In my deck, also improves Night Dealings, Braid of Fire, Gemstone Array, and Sun Droplet. If you run lands with depletion or storage counters like Mirrodin's Core or the Vivids, those also benefit.
Hive Mind - This combined with Enduring Ideal can absolutely WRECK everyone else. Few people's decks have enough enchants to survive not being able to play anything else. As an additional benefit, if you have this out first, it can protect your play of the epics, as you will get a copy of any counterspells that try to stop you, and can counter the counters.
Other non-enchantment cards I've got in my version that I think are fairly helpful:
Mirari - Twincast on a trinket. Copying Enduring Ideal and/or Eternal Dominion turns great advantage into near instant win. Two copies of an epic is strong. If you can combo with Rings of Brighthearth copying the Mirari activation, that's 3 copies of an epic a turn. With Paradox Haze that's potentially upto 6 copies played a turn. Copy Enchantment the Paradox Haze, and there's 9 copies of an epic per turn...
Legacy Weapon - In any 5 color deck, you just play this. It's that good. Repeatable exile of any permanent. Yes please.
Proteus Staff - Repeatable general tuck. It can backfire if your opponent draws into a big bomb, but for most decks, the general is the scariest creature around, and if the bomb isn't hasted, you can always tuck it again next turn.
Rings of the Brighthearth - Doubling up on activated effects can be very helpful. This primarily combos with planeswalkers, but in my deck, other significant targets include Mirari, Mind's Eye, Proteus Staff, Night Dealings, Rhysltic Study, Legacy Weapon and That Which Was Taken, plus the Words of enchantments.
Gemstone Array - Mana fixing and storage all in one. Especially good with Mirari's Wake and Doubling Season in play; tap one land for 2 mana, then put 2 counters on the array. If you're running Price of Glory, you can easily load this up during your turn in order to draw mana in other player's turns without destroying your lands.
That Which Was Taken - Make any other permanent indestructable. A few turns of this can make you much more resistant to the few board clears that do happen to target enchantments.
On the land front, consider some of these:
Crystal Quarry - Instant 5 color fixing for utility lands that normally produce :1mana:. Pefect for casting your general. Also combos well with Maelstrom Nexus and Legacy Weapon. Replace Kaleidostone with this.
Mistveil Plains - Put enchantments back into your deck if Wheel of Sun and Moon isn't out.
Mirrodin's Core - Can produce any color without CIPT or damage.
Serra's Sanctum - With this many enchants, this can be a huge mana producer.
Tolarian Academy - I run fewer artifacts than enchants, but still enough that this is a good producer by mid game.
I'm also a big fan of the Ravnica dual-bounce lands and usually run all 10 in any 5 color deck. While they are technically a bit slower due to the CIPT effect, they mana fix well and let me pack more mana into the same number of cards. This means I can more likely afford to play hands that might have only 2 or 3 lands in them, if one or two are bounce lands. It also means I can survive on 30-33 lands in the deck instead of 35-38, opening a few more slots for enchants. I try to offset this by making sure my other lands do not CIPT if possible and using a fair amount of artifact source mana.
Planeswalkers - The earliest version of my pure EI deck ran 12 of the 13 planeswalkers (all but Nissa, as she's completely useless in all 3 abilities without any elfs in the deck). The thought was that once epic, they were another source of free actions every turn. However, since unlike creatures and artifacts they're impossible to cheat into play once I've gone epic , I've cut back a little. Both Chandras, Sarkan Vol and Elspeth have come out, as being just too slow or irrelevant in decks that don't have any creatures and few sorcery/instants, though Elspeth may come back in for her 3rd ability. Garruk is on my current short list for replacement with some more lock out enchantments, and the two Ajanis are in only because lifegain and land destruction are both abilities I put an emphasis on. Nicol Bolas, Planeswalker, Liliana Vess, Tezzeret the Seeker, and Jace Beleren are all workhorses, though. Sorin Markov comes in or out depending on if I'm playing purely competitively or not; he draws a lot of hate/grief in casual games.
That said, if you like how the creatures are working out for you, I can suggest the following for cheating them into play post epic, as possible alternatives to Oath:
As far as creatures that might be interesting, due to their game changing effects, I'd probably try to favor board clearing effects, as your enchants already have the potential to seriously hinder almost any sort of control/combo based decks.
Early game, I feel I need significant card draw/advantage, until I can get my epics into hand and have enough mana to cast.
A quick note on the "Words of" series: Once you're epic, any of your previous card draw enhancement is mostly useless to you. These enchants turn that draw potential into extra "spells" each turn. Individually, a single draw replacement isn't that great, but if you've got three or four sources of extra card draw all going, you can get a lot of mileage out of these. If you're playing all those global draw punishing cards, these get even better, as they replace the draw and thus do not trigger damage for you.
For bleed effects, you're running pretty similar to what I do. Here's a few possibilities I've considered for my deck that you don't have. I don't run all of these at the moment, but I'm usually fiddling with a few of them, trying to find which combo works best.
As part of my lockdown enchantments, I run a few land destruction and disruption enchants. These are primarily aimed at making counterspelling anything I play a serious drawback.
For pure lockdown I have a few possible suggestions:
On the pure utility front:
Other non-enchantment cards I've got in my version that I think are fairly helpful:
On the land front, consider some of these:
I'm also a big fan of the Ravnica dual-bounce lands and usually run all 10 in any 5 color deck. While they are technically a bit slower due to the CIPT effect, they mana fix well and let me pack more mana into the same number of cards. This means I can more likely afford to play hands that might have only 2 or 3 lands in them, if one or two are bounce lands. It also means I can survive on 30-33 lands in the deck instead of 35-38, opening a few more slots for enchants. I try to offset this by making sure my other lands do not CIPT if possible and using a fair amount of artifact source mana.
Planeswalkers - The earliest version of my pure EI deck ran 12 of the 13 planeswalkers (all but Nissa, as she's completely useless in all 3 abilities without any elfs in the deck). The thought was that once epic, they were another source of free actions every turn. However, since unlike creatures and artifacts they're impossible to cheat into play once I've gone epic , I've cut back a little. Both Chandras, Sarkan Vol and Elspeth have come out, as being just too slow or irrelevant in decks that don't have any creatures and few sorcery/instants, though Elspeth may come back in for her 3rd ability. Garruk is on my current short list for replacement with some more lock out enchantments, and the two Ajanis are in only because lifegain and land destruction are both abilities I put an emphasis on. Nicol Bolas, Planeswalker, Liliana Vess, Tezzeret the Seeker, and Jace Beleren are all workhorses, though. Sorin Markov comes in or out depending on if I'm playing purely competitively or not; he draws a lot of hate/grief in casual games.