I think that an Indian faction would really stand out from the others because Buddhism is a very different world view than the western religions and I think that the Caste system would make for some interesting government and troop options.

In relation to the Yuehzi, I think the Eastern border of the map would also be less of an unrealistic boundary because the Indian factions did not suffer very much pressure from the Eastern front and we would not be ignoring the influence of other the Eastern factions like we must with the Yuezhi.