Argh you guys are missing the point of the thread.
I know Sigourney Weaver looks amazing, but this is more about whether or not Blomkamp's movie should use CGI to further tie it in with Aliens by making Siggy look like her 1986 self. Same with Biehn, who has differed in appearance more drastically since.
And forget about the practicalities for a moment here. After all, Arnold Schwarzenegger was digitally retouched for all of his scenes as Guardian in the 1984 segments of Terminator: Genisys. Lola, the company behind aging Hayley Atwell in Captain America: The Winter Soldier and deaging Michael Douglas in Ant-Man, says the technology itself has not changed since its first appearance - only the skills behind creating a realistic looking face. If we can have completely CG characters, films like Dawn of the Planet of the Apes, and looking at how damn good Michael Douglas looked in the beginning of Ant-Man, plus another few years before Alien 5 comes out, I don't think it's too far fetched to argue if this could happen.
My question is, should it happen? Would you guys be interested in seeing that? Would it be too forced to come up with a plot point to explain why Weaver and Biehn look different? Or nah?