I am working on an expansion for PMTW mod for some time. I have chosen English Civil War as quite easy to prepare and I thought of a very simple and quite efficient idea how to make some regions more important and to recreate somehow royalistic/parliamentarian support in certain provinces.
I think it is very useful for your mod as well, because it is civil war mod after all.
So basically the plain, usual infantry/cavalry types are prepared in three different versions with the only real difference seen in PRODUCTION/recruitment time to recreate three factors: - population of a province, - the number of unionist/confederate supporters in a province - how wealthy it was
So basically this way you will have 3 types of unionist/confederate infantry produced for 1,2 ( proposed average) or 3 turns.
This way especially large cities like New York will have its infantry produced in one year only, whereas some desolate and rather anti-unionist region will do it for 3 turns.
Of course there is a drawback too - the units won't be possible to merge, but it is worth paying the price I think.
This way some regions will have its importance fully represented in your mod and I believe it is worth paying the price.
Of course it is only useful for SP mode, but such war as ACW should get it for sure ! ;D