Should AVP3 happen? HELL YES! I finally saw AVP2 yesterday and I thought it was great in spite of taking place in Hickville USA.
AVP3 should take place in space, between Alien 3 and Alien Resurrection, and it should involve the downfall of Weyland-Yutani that was hinted at in Resurrection. Since the first two AVP films had the formation of Weyland-Yutani as a sub-plot, showing Weyland-Yutani getting what's coming to it by the Predators in AVP3 would be a great way to cap off the series and make it more complementary to the Alien series.