Really feeling like a tri-color cube can work. There seems to be just enough cross over synergy to make it work. I am going to attempt to list it all...
Jund: Likes sacrifice,1/1 counters
Naya: Easy. Likes big dudes and tokens.
Grixis: Likes sacrifice,graveyard shenanigans
Esper: Fucking tricky since it likes artifacts and that doesn't mesh well...
Bant:Like Naya, flexible so w/e.
Mardu: Likes attacking and sacrifice.
Jeskai:noncreature spells matter. Token makers go good here with sac themes,anthems,and whatnot.
Sultai: Much like grixis, except could easily be made more interesting with green dudes like satyr wayfinder and regrowth effects.
Abzan:1/1 counters and tokens. No problem.
Temur: Similar to Naya, probably needs some interesting blue twist.
So besides esper being a bit weird, we should be able to find quite a few monocolored and two colored cards that fit each shard/clan's theme. Between token makers, flashback spells, mill stuff, cycling, and whatnot, this could be a really sweet cube.