"Sure, a prequel's easy - the crew of the Nostromo were deliberately sent out there, with Ash programmed to bring back specimens - so someone's been there before, and they probably came to a sorry end... there's your prequel.
We've already had two shitty semi-prequels in the AVP "films" [I use the term loosely]... there you go. Prequel template established already.
Sure Ridley Scott will be involved... you think he's going to turn down a nice fee for Exec Producer credit, and the possibility of having some fan kudos with out having to actually do anything much? A hack like him? Of course he will.
Actually, the series isn't really much of a moneyspinner at all. Fox have claimed losses on all four films, according to their balance sheets. Big on home video, though."