While I didn’t vote for them, I’d love to see the Apache, Cherokee, Comanche, Sioux, and more Amerindian civs all eventually added to the game, albeit none in the Modern Age. They belong in the Age of Exploration. All of these tribes find their continuation through America in the Modern Age, and it would not make any sense to have them as separate nations contemporary to the United States.
All of these tribes were first discovered during the Age of Exploration, and the technology portrayed in that Age in the game is more on par with the technological advancements displayed by such tribes prior to their incorporation into America. It’d be strange in this version of Civ to see Cherokee commanders riding in Jeeps and Comanche helicopters flying around, however ironic that might be.