As well as releasing Alien, Aliens and Predator on Definitive Edition DVD, turns out Fox are releasing the final three sequels on Definitive Edition DVD too. I did a search on Play.com and noticed them. The three DVDs are slated for April 24, 2007 and the retail price is £12.99.
Artwork and special features are unknown but the DVDs are most likely repackaged versions of the existing versions.
Thanks to Mandalore for the tip.