As much as I like the idea of just adding areas and extending the time frame 50 years, i'm not sure that'd work quite as well. Espically for people who want to play certain nations who fall in power greatly during the 1700-1800 span. So I think a small focused campaign, with individual theatres as mentioned, similiar to Kingdoms is best.

The engine is mostly made for line fighting and fort battles (even if forts are broken) along with massive naval engagements.

Civil War has alot of naval engagements (i know it surprised me) and Napolean has that big one (With nelson). I don't know if other wars, such as african theatres or asian ones would let the naval engine use itself well.