Mexico, Cherokee(I'm stunned how this civ has yet to be playable), and Columbia.
Trail of Tears. It might not be the worst tragedy in human history, but it's one nearly every average history nerd is aware of and that alone makes it problematic. As opposed to the Long Walk of the Navajo which I, raised in Arizona, was never taught in American history classes.
I'm not saying I agree with it because the Cherokee have a lot going for them design-wise, but just the likelihood that ten times as many diphorsehockys might make "Trail of Tears" YouTube videos as they would "Long Walk" videos is why we likely won't have the Cherokee in the game. Plus the whole fact that there haven't been many positive U.S.-Cherokee relations to balance it out, while the Navajo have the whole "spy" angle going on as well as holding the largest patch of tribal land in the U.S. comparable to a pseudo-independent state. It's a lot easier to point to resonant things in the public consciousness indicating the Navajo "bounced back."
After we get a sorely needed western US civ, I wouldn't mind a Cherokee civ at all. I think they're the best option for the Mississippi region hands down. But they are about as likely to happen as Armenia, or Israel, or Tibet. Too problematic.
OH and to address criticisms about my Mexico/Mexica hybrid civ, the cultural legacy is there. Roughly as much as India's connection to Ashoka, despite India having plenty of ethnic conflict as well. But I'd rather discard the Aztecs altogether and just have a "Mexico" civ with some vague Aztec flavor. My reasoning for this is that the happy medium VI seems to be striking is to have a modern imperial power (United States, Canada, Australia, Brazil), juxtaposed against an aggressively expansionist and influential native people filling out the rest of the map (Cree, Mapuche, and in the past civs like the Sioux and Shoshone). It seems a more elegant and balanced representation to have the Maya, vicariously representing the distinct and aggressively independent Yucatan region, juxtaposed against Mexico as opposed to the Aztecs which they have no real relationship with. That way we could have:
* America and the Navajo/Apache/Shoshone/Whatever
* Canada and the Cree
* Mexico and the Maya
with additional options like
* Brazil and the Guarani (vicariously representing the Tupi)
* Australia and the Noongar
In a game with such limited options, and particularly a game like VI which is really trying to increase native representation of peoples
outside the United States, this seems a very fair way of spreading the love around. So I'm quite disappointed they didn't go this direction with Mexico.