An ancient era scenario does sound tempting, as does a Roman era one. Now that we have corps and armies, Napoleonic or Great War (WW1) scenarios would be cool too. I enjoyed the steampunk scenario in Civ V quite a bit, so there's that. Perhaps a colonial America/Revolutionary War scenario? American Civil War could be ripe for a steampunk treatment. Not my area of expertise but there must be some real interesting scenario possibilities set in the Renaissance or as fantasies built around DaVinci type inventions. War of the Worlds, anyone?