I cant think of what else they found that wasn’t in the special features already included in the Anthology collection. I don't believe we've seen everything. The amount of footage that was filmed - there must be more stuff unreleased.
The announcement specifically mentions O'Bannon's archives being accessed for the first time. I don't think this whole Memory thing is something I know of. If it is, I can't remember it.
I would like to see more from Giger's archives - specifically, behind-the-scenes footage. Who knows how much film footage there is that didn't make the final edit for Giger's Alien
I don't recall seeing any behind-the-scenes footage from the deleted cocoon scene in the Giger's Alien
documentary, yet footage (of the crouched Brett egg figure with the missing eyeball & dressing the cocoon set) turned up as clips in The Beast Within: The Making of ALIEN
The Brett egg and set dressing footage look very much like Giger / Mia filmed outtakes from the Giger's Alien