The 50s, USA. There would be the standard ones, and there would be the superhero NiceGuy. No wait, noone would play that, because NiceGuys finish last.
Just a squib.
There could be India, there are numerous myths in Hinduism, there could be Chinese, they have their own, as do other Asian cultures, though there is predictable similarity in some of them, ala Greek/Roman copy, there are probably African (Hey! A chance for an African civ!), as well as Native American and South American...Since it's plain that different timelines will be overlapping, why not go waaaay back and pick up some Cro Magnon types, with a SpiritCaveBear hero (try fighting a cave bear: those boogers were 7-8 meters tall, no kidding. That's a lotta bear.) Invent Atlanteans? Pangaeans?
Who can say? It might be that the civs chosen are enough to make a good game.