The fact that there's going to be a Prometheus 2 is such a shocker that even Fox doesn't have much of a plan for it, according to a Bloody Disgusting report. The site says that the studio is taking meetings with just about every writer in town trying to figure out where the hell to go next, as absolutely nobody has a vision for the thing.
The fault, the report states, is Damon Lindelof's. When he came on to rewrite Jon Spaights' draft of Prometheus he turned the film into the first chapter of a trilogy, but then he left the project. Probably, it seems, because he had no idea where the trilogy should go after the finale of the first one - something any fan of Lost can tell you was in the cards. Lindelof has strong concepts, but bringing them home has never been his strong suit.
I can't verify everything in BD's report, but I can tell you I know that Fox has been taking many, many meetings with screenwriters, and that screenwriters have been pretty much bringing in their own pitches, not working within an established frame. I actually don't think this is a bad thing, and the Exquisite Corpse nature of the sequel could give the new writers a chance to make serious course corrections. But that's on the creative end - on the studio end the up-in-the-air nature of the sequel really opens the door for tons of terrible ideas, executive tinkering and Ridley Scott dithering. Maybe Prometheus 2 will die on the vine. More likely, Prometheus 2 will end up being really rushed and half-assed.