I never liked the idea of a prequel to Alien. The origin of the derelict ship should be left a mystery, because any kind of answer would likely be disappointing.
That said, I would like to see another movie set in the Alien universe with the Xenomorphs (and no Predators!). The question is, what kind of story can be produced that would be interesting and unique?
That was the problem back in the pre-production phase of Alien 3, although I do think the third film ended up being quite unique, if very flawed.