The Keeper wrote:
I also wouldn't go with Khan again so soon. Over the course of the next few films, let the events of ID slowly stir up the best of the regular OS species to the point of all out WAR then unleash Khan forcing them all to work together against a common foe. [/fanwank]
The next one could very well be the last one for this team. Or at least for a lot of them. Contracts are ending, new negotiations will have to be made.
They don't really have the luxury to leave things for other future possible movies.