So I may be wrong but I don't think there will be any civs as powerful as say Aztecs, Korea, Nubia et al... Which I'm ok with. Different play styles opening up seems much better than power creep.
If I am wrong then my prime suspects would be Ottomans and Inca. Ottoman millitary is good but the Ottomans are a bit too slow to get their uniques for me to expect them to be a top tier domination civ. For the inca it all depends how big the early growth/production advantage will usually be.
As for the others:
Hungary could be good, I'll have to play with levying more.
For multiplayer Canada are probably the worst civ in the game, as they will just be perma-denounced but the no surprise wars could make them one of the easiest civs at high difficulty.
Maori seem like the opposite, the more settlers an AI starts with the tougher they will have it... But at lower difficulties they may dominate easily.
Phoenicia look like fun but kinda niche.
Mali could also be a bit powerful, but they bend the rules so hard it's tough to know how much without playing them.
I guess Sweden will rank alongside Kongo in most tier lists. Both specialized in the same thing means they will probably stack up similarly.