There was an ALIEN 5 script that was written in 2000 by a screenwriter I'd never heard of (forget his name). It was supposedly so horrible that it never even got a second pass.
Despite the fanboy yearnings, I somehow doubt Ridley Scott will return to the franchise. In all the recent interviews I've read/seen he comes off as very ambivalent about it. James Cameron, however, seems much more likely.
Cameron had actually started developing ALIEN 5. When he contacted Tom Rothman and the other execs they apparently didn't even want to hear his pitch/concept because they thought ALIEN VS. PREDATOR was where the franchise should go:http://www.bloody-disgusting.com/news/5777
Keep in mind that this interview was from 2 years ago. I expect that when AVATAR comes out (most likely a hit) Fox will go crawling to Cameron to ressucitate the franchise. Especially since AvP 2 bombed. I suspect if he does it, someone else will direct.
Just keep John "I'm a franchise whore" Davis from coming anywhere near it.