I think that there are 3 choices :
1. If they would continue making games like in the old line(shougun,medieval,rome) then medieval 3 would be next,but since they announced that it will pass a long time before they make something with 3 in it next won't be medieval 3.
2. They listen to the majority and make Rome 2 total war.
3. They make something completely new a surprise us all.
Eventhough I am for Rome 2 I think that they will make something new.