This would be a lot of fun! I don't think it would just be 1/3rd of the field playing miracles. Stuff like BUG decks would be good if the meta is Miracles-combo-chalice decks. I could see a good team being something like BUG Delver, Death and Taxes, BR Reanimator.

I have not played unified before, but like 6+ years ago I played Legacy 2-headed giant in a tournament and it was awesome! It has similar rules (only 4 copies between both decks) but unlike unified it is a 2v2 player game with just 1 game per match. Me and my teammate won with Burn and Merfolk. But there were some cool combinations people came up with, Dredge + Landstill being one of the scary combos when there is no SB games.