Are you all possibly forgetting something quite fundamental? All the ancient civilisations you propose are fine - any African, Persian, Polynesian, Middle Eastern, whatever, but they would have to be a global ''power'' to progress to the Industrial, Global & Space Ages in this game.
For example, did the Zulus feature prominently in the European theatre in WW2? Did Egypt or Turkey or Somalia land on the Normandy beaches? Do these nations have nuclear arms??
I'm not condemning these nations or talking them down at all but I'm looking at it from a
Dominations perspective. (FYI, I was born in Africa so I'm not speaking with any kind of bigotry .....)
The nations have to have ''somewhere'' to go in this game after the Gunpowder or Enlightenment ages - simply suggesting that players change nations when the ''historical relevance'' stops is not very practical. For that reason America or Russia would have to be the next logical additions.
Actually, I don't have a problem with Persia or India as new civilisations but I think the history in this region & the political/religious turmoil there at the moment might be a little too sensitive for the devs to include them - which is a pity cos I think the Iron/Classical/Medieval, etc, ages would have some really cool looking buildings.
But I have to wonder what an Iranian tank would look like if it wasn't for the British, Russians & Nth Koreans .....