Would really respect a historically accurate mod... That'd be something. Get rid of the elves and orcs, and give room to the real stuff.
Also, if the map is editable, you could include a lot more east in it. For persian campaign, you'd need to make it all the way into india. Just make sure there is no reason going north of india, since there should be pretty much nothing. A bit like the big african province in MTW which was empty. Even if that one might've been wrong.

Will it have skirmishers in non-populated areas? Remember the 10000 men march? The returning to home, that stuff.