My ideas are Renaisscance Total War which would span history in the game from the 14th to 17th centuries. I say this would be a nice game to fit before Empire Total War. Medieval Total War II does this, but Renaisscance TW would have naval battles as well. You could replay the Battle of Lepanto, for one.
The second idea I had would be a game called Imperial Total War, which would cover history after Napoleon to say 1905 at the end of the Russo-Japanese War. Have it end before the onset of wide aircraft use. I believe the Total War engine could portray these conflicts quite nicely. Steam, iron and artillery, replacing, sail, wood, and cannon, it could work. And if its not the case to go all the way to 1904-05, then surely to 1902 to the end of the Boer Wars. The Wrights make their famous flight in 1903, so 1902 would be a good year to end the campaign. Although, I would love to see the Battle of Tsushima and the Battle of Port Arthur in game as well. With this an an American Civil War expansion would be an awesome standalone addition to Imperial Total War. Just as The Fall of the Samurai will be for STW2.
I like these ideas better than a Rome Total War 2, but I'll take what I can get. RTW2 will be quite interesing, because of the addition of being able to play out early naval battles, which were quite intense affairs. RTW2 also opens a door to a possible expansion for the earlier Greek Wars, or a better second Alexander the Great campaign. Anyway with these three games, RTW2 along with my two ideas, they'd be busy for some time to come. I wonder how I could get a hold of Creative Assembly and tell them about my humble thoughts? Hopefully they have thought of those two ideas themselves, they are obvious choices, which would work using the Total War engine.