Leobon
I'm a Townaedo!
One rather radical idea that I have include a continent specific resource that will limit or allow the building of some types of units. Let me elaborate.
Rather than splitting the world into an "Industry" half or "Colonialism" half, Why not have an "Africa", "Asia", "Australian", "America" and "European" sectors of the map. Rather than being able to build "Colonial Infantry" everywhere as long as there are "Colonialism", why not take "Colonialism" away from Africa (for example), put an "Africa" resource for the continent and allow the colonial powers to build African units rather than the generic colonial infantry. This way, we won't need the wonders to be built for the various askari units.
However, this will require a lot of work to be done, including revising the units' cost, units' stats, the wonders, putting in new resources and of course revising the boundaries to confine these resources.
If El Justo if interested, I'm willing to offer my help. A downside would be a delay in the launching of the latest version, but a few days of refining and tweaking I think will bring about a more than proportionate return in terms of gameplay and realism.
Improvements and wonders are keyed to industry and colonialism. Continent-specific resources would negate all of that and put the entire building tree into complete chaos. There's not enough slots. Plus, you'd have African colonial buildings, Asian colonial buildings, South American colonial buildings, so on and so on, and that would be impossible to do.