Let's just say for example that the next AvP movie takes a whole new direction, completely ignoring AvP and AvP:R. Would you prefer it if the Predators already knew about Aliens existence? Or not? Also, how would you personally approach it if you were the Director?
I think that it would be much better if, during their first encounter with one another, the Predators completely have no clue. For instance, aboard a space vessel, the Predators have gone rampant, skinned some cronies and generally kicked ass. Then, suddenly the tides turn as the mighty hunters see their prey being dropped one by one. All the people in the room are being brutally murdered, dragged into vents and impaled, though the Predators cannot see a thing via Heat vision.
Then much later into the movie, after they have seen their comrades fall by these...invisible ghosts, a lone Wolf discovers a small device that the Humans recovered from the Ship along with the Aliens. His Mask recognises it, locks on and begins "decoding" it. Eventually, his Visor automatically switches, only for the Predator to see an Alien right in it's face (a WTF?! or startelling moment, if you will.) From there, an epic struggle takes place, as his mask begins sending the Vision mode to the Predators still alive...