I don't think Ridley will direct a Prometheus sequel, he may be attached as a executive producer or a consultant, for script and design advice. Scott has got many other projects up his sleeve such as the blade runner sequel, I would love to see Fincher return but fox would have to give him free reign and I can't see that happening, even with Tom Rothman gone. A budget for the sequel would be smaller than the original and fox love their let's push for a pg13 mentality, which I don't think directors such as Fincher would conform too. I would like to see Christopher Nolan have a shot, but a sequel would need to begin answering the questions raised in Prometheus. We need to see a lot more of the engineers, how they live and their culture etc, are they all aggressive and why do they create life forms, terraform, then wipe a species out. These are all very interesting facets I would love to see explored.