cybrxkhan
Asian Xwedodah
Cherokee have been mentioned a couple times.
As for the Mississippians, the primary problem is that we lack a leader or language; the old culture had largely collapsed by the time we were able to record the details of their descendants.
There are several groups around today who are descendants of the Mississippans such as the Natchez, though I think it might be hard to find a decent voice actor for them oter than a university-trained linguist/anthropologist or something (then again we had Attila speaking Chuvash from Gods and Kings, so who knows?).
Speaking of which, I'm interested in how they'll handle language for some of the possible civs. For instance, if Vietnam's in for whatever reason, I'm interested in what dialect they'd choose - it shouldn't be too hard to find a decent voice actor for either gender given the large amount of overseas Vietnamese in the US (not to mention there is a somewhat developed Vietnamese media here), but many of the Vietnamese here (to my knowledge) speak with the southern accent, which is stereotyped as being the Texan-like accent of Vietnam, while the northern accent is stereotyped as the "cultured" and "proper", British-like accent - and then there's the Central accent, which no one understands. Ideally in terms of historical "accuracy" the Central accent would be the best, as to my knowledge it's linguistically the closest to middle Vietnamese, but in terms of immersion the northern accent would be better given that pretty much any potential leader for the Vietnam civ comes from the north, and it's seen as the "proper" accent by some Vietnamese.
What about Hungarian, I'm wondering? Is there a specific dialect or accent that would suit a Hungarian leader more?