As Scott revealed during the Alien: Covenant press tour, Alien 5 wasn’t even really that far along, as far as he knows.
Ridley Scott planned at least one more prequel movie that would take place after Alien: Covenant and bring us to the events of the original Alien.
The District 9 director essentially willed Alien 5 into existence a few years ago.
While working with Sigourney Weaver on Chappie, he came up with an idea for what would have reportedly ignored the events of Alien 3 and Alien: Resurrection.