I think a Civil War period would be a Saga title, really along with anything else that was in the Kingdoms expansions. I don't stake my money on a Civil War or Crusades campaign officially happening either, but time will tell. If anything I think it will be a new full bore gunpowder title (Empire 2) or possibly something in the Medieval period.

I want to say that the next major historical title will probably bring true technical changes, but we'll have to see there too.