While I don't doubt that Survivor mode is going to be a great deal of fun, the lack of any equivalent for the other two races is a little disappointing. The is particularly true for the predator, seeing as it was playable in the Skirmish mode of the original game. So after putting a bit of thought into it, this is what I came up with:
Name: Rite of Passage
Players: Up to three player-controlled predators (otherwise AI controlled).
Enemies: Waves of increasingly difficult aliens, culminating with the queen.
Basically, the gameplay would mimic the premise of the first AvP film. Now hear me out before you start hurling abuse. Each predator player starts out at a different (randomised) entrance in a pyramid similar to that from the first film. Initially they are equipped only with their wrist-blades. As they proceed inside, they encounter waves of aliens with steadily increasing numbers and frequency, and also gain access to higher level weaponry at designated points. What makes it interesting is that the pyramid would rearrange itself every few minutes, making your progress through the pyramid restrictive and chaotic. An unfortunate shift may result in you being trapped in a dead-end for a while, having to fend off the aliens until an alternative path is opened.
An ultimate destination (if one is needed) could be a central arena where the first predator to arrive is able to face-off against the alien queen. This chamber would then be locked to the other players for the duration of the battle, relegated to holding off the aliens in the surrounding corridors. Should he prevail over the alien queen, then the player wins the match. If he should fail, however, the chamber re-opens and other two players are given a chance to take their turns. You could also have it so that, wherever a predator player happens to fall, a predalien is spawned in that location, creating a nasty surprise for anyone who happens to stumble across it later (unless they are defeated in the queen chamber).
If the internal reorganisation of the pyramid were done just right, creating an effectively random path in each subsequent game, you could even get away with having a single map. The result would be a game mode that shares some of the survivalist feeling of the Marine equivalent, but overlays this with a competitive dimension which really suits the predators. Should they meet up during their random progress, players would face the decision to either stick together and help each other reach the central chamber, but thereby run the risk of handing victory to their ally, or else leave them to fend for themselves and run the risk that both of you will be overwhelmed before you ever reach it.
UPDATE: Corrected the typo in the name of the game mode.
