Mexico won't happen over the Maya, and it won't happen alongside the Maya. But it would sell like hotcakes so it is one of the most likely civs that would make DLC or expacks after the third one. And I am not wondering at all. The Haida are competing with comparables like the Tlingit and Taino. The Mughals are competing with comparables like the Timurids. And Vietnam is competing with comparables like Burma and Siam. Absolutely none of these are clear cut frontrunners and actually I would say all three are not the frontrunners in their respective races. So I find your wondrance perplexingly presumptive.