I thought the Trebuchet was in the Middle Ages (I admit,this I know from AoE2
) ?.But as they don't say xxx Trebuchets,I guess they'll be available for everyone.
Mayas,Incans,Sumerians we know FOR SURE.
Remain 5,let's see what we can guess:feudal Japan could be Japanese only,but it could be a good hint towards Dutch and Portuguese.About the crowded Europe:Already after vanilla civ it was too crowded and they still included Spanish,Vikings and Celts,so why shouldn't they do it again.
WW2 could mean Polish,but of course Poland has much more history than these 6 years.
As calgacus asked about another big civ market:I'm pretty sure it's also in SE Asia and we have Jade,so it could be Thai,Khmer or Malayans.
I hope they include another African one like Songhai/Mali,if just to make it not possible for Zulu to grow too strongly before meeting Carthage/Egypt.