If I were abducted, held at gunpoint, and told that I would earn my freedom, and $100,000 USD somehow tax free (I'm not cheap) if I wrote the script for Alien 5 and it had to include:
-Ripley 8
-The above encountering Shaw and David.
-The origins of the Alien
I would be in that room a long time, or possibly dead after being shot during an escape attempt.
If, however, I was granted latitude on the last plot point I would, as I'm about to, hack out something like this:
-Ripley 8 would be tracking down the "alien homeworld" to exterminate them "once and for all!"
-Shaw and David would be finally on the Engineer homeworld having adventured through time and space. There they meet Ripley 8, who just stumbled upon it.
-The Engineer homeworld is in ruins. Yes, the Alien did it. They learn that the Alien is very adaptable when it comes to reproduction especially after driving a spacefaring race back to something like a stone age. Anything goes, and all of it is horrible.
-The three team up when they conclude, via completely unbiased analysis, that the Engineers created the Alien and were predictably murdered by it.
-They learn of a remnant of Engineers out in the cosmos. Shaw wants to ask Why more plaintively than ever before, and Ripley 8 just wants to murder them.
-They find these Engineers holed up in some fortress, with countless goo-related traps. We'll need extra human characters to suffer the body horror so our plucky trio can get through unscathed.
-These Engineers are clearly extremely paranoid and seem to be on the verge of ending themselves. But when Ripley, Shaw, and David finally appear before them they seem relieved, and quit talkative.
-They reveal that they simply found the Alien (though not anywhere they believe is its homeworld) but on some other world ravaged by it (where they learned that civilization had once found the Alien as well. They also reveal that the black goo originally had two purposes: first to immunize lifeforms against the Alien. Second, to serve as a weapon against the Alien directly. They failed miserably on both accounts because they used too much of the Alien's DNA in making the goo and it proved just as adaptable. That or something made to fight a monster (surprise!) turned into a monster itself. They hang their heads in shame and say "we were wrong". Shaw looks crestfallen that someone stole her thunder.
-Their story told, the Engineers go into hibernation after telling our protagonists to go look in a nearby vault for "the truth/origin/destiny of the Alien" (David has trouble translating that bit). In that vault we see a map of the galaxy that shows that the Alien is effectively everywhere. Roll credits.
I would be released and naturally not paid. My script would go on to suffer so many rewrites it ended up as a Gremlins sequel.