The whole thing is a joke. On the one hand you can easily say AVP is only canon to the Predator series, for instance, but this business of subdividing things and saying for instance that Promtheus through Blomkamp's film is the core story or just alien thru a:r is another or alien thru blomkamp or avp through a:r is canon... And then saying "Ooo it's a MULTI-VERSE" is just putting shit in a nice package. What it is, is simply - a mess, thats all. It was caused by Fox being opportunists, and jumping on whatever works in the moment, instead of calculating things, the way they did with Star Wars. And I would argue that Lucasfilm and Disney were responsible for that stuff.
Has anyone considered that maybe Blomkamps film will only undo Alien 3 or that it will ONLY remake Alien 3 and Ripley and Hicks will be prisoners at the end so Alien Ressurection is still canon? See? They can do that now. What I mean to illustrate is there is no turning back from the mess they've made. They can just do whatever and if this retcon thing is the way it is, they can just do whatever next kind of installment will generate the most profit at any given time. Include Predtors in Alien 6! Why not? We can just ignore it for the next one as soon as it isnt profitable again and then start from two movies ago or, or, or. Options are wide open from here. Multiverse? Please. A turd by any other name is still a turd. James Cameron was right Avp destroyed the integrity of the franchise. David Giler was also right, A:R ruined the validity of the franchise. But they wont fix it, because they found a way around that risk. And they are applauding themselves for it because it worked out from a business sense. The cards were played well. Now they have this massive tent-pole of two films coming out that everyone will see. Thats all they need to worry about. They f**ked it up and dont intend to fix it because once you make this kinda mess and havent lost the profits, you have opened up all options to capitalize on whatever new idea will sell. It's a resounding success that is working in their favor. Why would they fix it? Why close doors that are only flooding the house with money?