Educational software is a pretty huge market and you've already done a lot of research...
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EU and Heart of Iron are already pretty good by themselves for historical geography.
It not perfect I admit but hey it still educational if you do some encyclopedic search to go along with it. (I admit adding an encyclopedia in the game would be nice)
While 'good' is nice it's not real geared toward EDU, and EDU software can sell MILLIONS and MILLIONS of units if it gets picked up. And probably less work than a good game. (Well less software work, more business/sales works in getting ppl to use it..)