What I'm curious about is modding issues. For instance, you say that the colonial nations will only occur in the Americas. How does the game know that a particular European colony is "in the Americas"? Is it a property of the region (set in \map\region.txt), the continent (set in \map\continent.txt), or does the game engine check whether the province is inside the "rectangle"* that the game uses for determining which part of the world will be randomized if the player uses that option at game start, or ??? 'Cause if it's in the region file that would be really awesome for modders.
I really hope the colonial mechanisms are bound to the colonial region map and that you can add colonial regions elsewhere through modding.