I think a sequel so soon would be EXTREMELY BAD. There are tons of people and modders working on big projects, and they're going to be real pissed if after just a few months there's a new game that everyone's switched to.
An expansion pack using the same engine would be ideal. Modders can very easily port their stuff to it, and it lengthens the life of the game.
Plus, I highly doubt they would make a whole new game so we can find out what happens to Tavion. An expansion is much more likely, especially considering they made one for JK.