I'm still struggling through the early stages of learning how to play this game, so anything I say falls under the rubric of raw initial reactions.
There's a short list of nineteenth century wars I really want to see simulated by the game model. Taiping rebellion and the last phase of the Opium Wars happens to be at the top of my list, but I'm not holding my breath on that one.
But what I really want to see are the Guano Wars in South America. There may not be much room in the system to show former colonies duking it out over natural resources, but the first act of the Guano Wars involved Spain making an unabashed grab for South American Nitrate resources that probably included the first transatlantic use of ironclads. You don't get any more imperialistic than that.
Spain may have been a shadow of its former self in the 19th century, but any way you look at it she was still a major (and occasionally interventionist) colonial power until her run-in with the United States. She needs her own permanent slot in the Grand Campaign, even if no one ever cooks up a scenario involving Peru, Bolivia, and Chile. Some things shouldn't be left to modders.