Personally, I think that the Predator culture has been explored enough as it is. So if anything, I think something like that should be left alone and well enough. We already know that there are different clans with different customs, and that's fine but like someone had said, keep the some of the blanks filled in to let the fans do their own thing. We don't need to see their politics, we don't need to see their society because we know that they are a clan based society similar to aboriginal tribes (think Native Americans, Maori, etc).
I wouldn't mind seeing new technology, and I wouldn't mind seeing alien creatures but as far as alien worlds are concerned.. Please, no preserve planets. That was just f**king bullshit which cheapened the thrill of the hunt. It took away the challenge and thrill which the first two movies even established, and if you count the first AvP, then that movie too. If alien worlds are to be involved, I wouldn't mind seeing something similarly to what the scenarios of Pitch Black and the third Riddick movie showed.
As for crossing Prometheus, Alien and Predator over.. No. I think the comics which are doing that is enough, and I agree with Bio Mech Hunter in that the possibility of Engineers being involved with the Predators aside from an antagonistic relation is a route we don't want to go down with. I know someone joked but.. the idea of it is.. No.
But considering that Shane did final rewrites to the first film, I trust him. I'm cautiously optimistic and with Fred Dekker on board.. well.. Right now Dekker is a mixed bag for me. He did two awesome movies which I really liked, but one movie which.. leaves me with some doubt is the fact that he did Robocop 3. But I am really hopeful.. Truly hopeful.
I just hope it ignores PREDATORS.. or boots it.