I heard somewhere that Fox said that Alien, Aliens, AVP-R, and Predator 1 are all slated for release on Blu-Ray sometime next year. There are no plans to release Alien3, Alien 4 or Predator 2 in HD at this time.
Personally, I want a HD quadrilogy set. I know the extra content wont be in HD, but all the films can be, and I would sure buy it again.
I think i have bought the movie Aliens at least 8 times. I have 3 different VHS releases, 3 DVD versions, 2 Laser Disc releases, one opened and one still in the wrapper. LOL