I read your series today and I really liked them. Your opinions are well supported, and your analysis covers each keyword from many different aspects in a broad view.
I have one correction to make though. Suspend wasn't the first ability to use the exile zone in a way that no other card could, imprint in Mirrodin block did it first (albeit in an unexciting and not very memorable way). This mechanic still has quite a lot of untapped design space.
I don't have an idea what the first keyword would be. Trample is one of the most beloved mechanics of all time, that plays well and has history. However, it's not very innovative - many attacking/blocking mechanic have been made alongside it from the very beginning, and it's not as resonant as flying.
OTOH I definitely know what will make the worst ten keywords of all time: Shroud!
Do we want to discuss the cards presented in the OP in this thread?
Aetherling is exceptional in control mirrors. I found it also narrow, and too slow against midrange decks. It is the best inevitability tool, but most control decks have enough ways to win the game with utility bodies and planeswalkers, so it is not a necessary piece as I once found it to be.
Stoke, Blade, and Meren.
Rimrock Knight is a fine dude. The better lines of play with it are:
T1 one drop, T2 pump + another one drop
Turn three and up, playing both the pump and the body
The catch is that the body is quite weak for a two-drop. Overall it is a card that always tables and is about the 4th worst red two-drop we play. This gives Knight some longevity, and it is not currently on the chopping block, hence it is not marked as 'weak'. I do think Knight is more interesting than most two drops and has surprising synergies, which are slight points in its favor.
Looking at your list, I might play him over Abbot, Stormblood Berserker, or eventually Kargan Intimidator (I have little testing but low expectations).
Sarkhan > Terror > Conscripts
Divest > Despise > Appetite
Shatter > Never
Games > Surrak > Sovereign
Liliana > Ob
Field > Realm
Champion > Oracle > Mage
Tribunal is better in aggro, Quarantine is better in control, in midrange they are about equal.
Marauders > War-Name > Ire Shaman > Harsh Mentor
Force > Censor > disruption > spike > pierce
Unleashed and Masterless
I think Heart is the best by quite a bit. It is playable in more decks, castable with more hands, and fixes colors in a relevant stage of the game. Even in decks that would play Gilded Lotus, I never want to cast my first ramp spell of the game later than turn two.