Crackdown and APB's Realtime Worlds shall unveil their next project, of which they're all "very excited" about, next year. It's believed to be another MMO.
The "ambitious" nature of the game meant that they had to see APB released first, in fact it was the project that Realtime Worlds was originally formed to make. That's all they're saying.
GTA creator Dave Jones made the revelation during his keynote at the GameHorizon conference, and would only give out teases as to what it might be. It's "a very ambitious project" that his whole studio team is "very excited" about.