The way the colours are balanced there will be no WU or GB cards in the set. This is a world with no clans that cover those combinations. Of course Vraska is a exception because she planeswalked from Ravnica. I think this is a cool change. It fits an 8 player draft perfectly. You can either have all 8 players playing the 8 supported 2 colour combinations, which would lead to 3 Dino drafters, 3 Pirate, 1 Merfolk, 1 Vampire, or you could have two for each clan. Both break down perfectly, unlike the 10 guilds or 5 colours of a normal draft, which leads to an imbalance in an 8 man draft.
This means starting a draft with R is a slight advantage because you can pair it with any colour, whereas the other 4 have an unsupported combination.
Here is Shaun McLaren's more controlling version that he played at the PT. Though he says he likely should have included some Hangerbacks to trigger Avacyn. I think I will build one between the two.
I'm also noticing there will be no white Eldrazi and all white archetypes are Ally related. So if you are drafting white you can prioritize Allys. The second most focused colour is black with three of it's archetypes being Eldrazi so you can be pretty safe prioritizing them if you start off black. G, R, and U have very varied archetypes based on what you team them with so may be slightly more skill intensive to draft.
Edit: I guess UW is not an Ally colour pair so W and B are evenly focused, split 3 to 1. Also, blue is the only colour with no Ally archetype in it's pairs.
So we know WotC seeds limited environments with gold uncommons to point us towards what the pair should be doing. We now know all 10 gold uncommons. So here is what BFZ limited is intended to be:
Looks good. With 3 Crippling Chills we may be able to get away with 17 land. I would like to get a 13th creature in there (Witness of the Ages). However I just worked out the mana and I think this deck need 5 Mountains, 4 Islands, 4 Plains, which would not leave room to add the Witness.
I may actually replace Quiet Contemplation with the Witness as I have not had good experience with the card, but this might be the deck for it.
This means starting a draft with R is a slight advantage because you can pair it with any colour, whereas the other 4 have an unsupported combination.
Edit: I guess UW is not an Ally colour pair so W and B are evenly focused, split 3 to 1. Also, blue is the only colour with no Ally archetype in it's pairs.
RG = Landfall monsters
GW = Ally tokens
WU = Awaken tempo
UB = Eldrazi Processor control
BR = Eldrazi agro
BG = Eldrazi Scion tokens
UR = Eldrazi cost reduction
WB = Ally Vampires
RW = Ally agro
GU = Converge
So we got 4 Eldrazi colour pairs and 6 rebel colour pairs. Each are spit half and half between enemy and friendly pairs.
This also means UB is likely the color pair that is focused on Artifacts this set. In the first MM it was UW.
I know it says they are not necessarily in but I think they likely are.
I may actually replace Quiet Contemplation with the Witness as I have not had good experience with the card, but this might be the deck for it.