As the Atlantic would take up loads of the map, the scale of the mini-map would be even smaller to that extent that fans of the mini-map would need to press the zoom button more than five times to be able to discern the terrain reasonably well. So, the assumption that there will be an Aztec mini campaign is likely.

Came to think of something... it would take years to learn all the names of the Aztec cities, units, generals and buildings. And people used to say that Roman unit names were hard to spell when RTW was released...