In classic Age of Empires III we have some unplayable native tribes, with 1-2 unique units each:
Religious movements in Asia:
Personally, I would like to see some new native tribes for Siberian map (which is big and empty). For example:
Yakuts with unique heavy cavalry lancer:
Chukchi with unique armoured archer and spearmen:
And you? What new native tribes would you like to see in AoE3 DE?