The Alien movies have a beautiful tradition of casting actors that aren't drop-dead gorgeous, super hot, muscle bound, mega fit, overtly attractive etc. The tradition was broken in PROM, and the AVP movies don't even count ;p
Actors in Alien movies are people of all ages; hard working everyday people with regular looks, where's others have very characteristic and distinctive face with proportions or features that hardly would win them a beauty contest. The closest thing we get to pretty boys and pretty girls are The Girl/Boy Next Door characters, like Hicks or Call.
I really hope A5 will stay away from the young-hot-n-sexy trap. I would love to see Willem Dafoe for example.