We know that Napoleon had a Piece of Eden in his possession at some point, so it's likely that he was a Templar. Even if he wasn't, he's just too juicy a character to not be involved in the Assassin's Creed saga in some way. And as dictator of France, he was known for having an extensive network of spies around Europe, which would be a good environment for an assassin to work his magic. And since the events of ACIII seem to be focused around America during the Revolution, it would make sense to have a follow-up set during the Napoleonic Wars (possibly even the War of 1812), where Connor could see the events of the Templar-Assassin struggle on an international scale and get a look at its effect on the dynasties of Western Europe.