I don't think I'd enjoy a world-scale game, or even the expanded map proposed in the original post. The problem is that CA doesn't have infinite time and resources, to develop something as rich as RTW at "ground level" for the whole world, or even a large chunk of it.... which is what you'd need for this colonization idea.

I love seeing all the detailed differences between units and buildings from different cultures in RTW. It helps with immersion, and keeps me interested. If CA tried to model a larger part of the world's geography and local cultures, then (given fixed programming and art resources) it seems to me that we'd see a lot more generic units.... just a few Amerindian tribes in North America, for example, instead of the huge number of actual tribes in the area, all with unique cultural differences and styles of combat. Same thing with Africa, or the Caribbean. Sure, it would be an amazing game if they *could* model the whole world at RTW's level of detail. But I don't think we want to be waiting 10 years for the next version of the game.