The concept sounds interesting, but theres a few things to consider. For the aliens and humans, what will the "gate" look like?
Maybe it should be an actual gate for the humans, maybe make it look high-tech and such. What about for the aliens? Possibly some giant wad of flesh that opens up when entities comes near it.
How big and wide should each gate be? Should it let humans/aliens jump on it and attack from there, or will that introduce more camping? If we don't want that to happen, what will we do to stop humans/aliens from getting on it? Theres several ways of doing so, humans and aliens could build structures to make a staircase to it, or jumping off a ledge and landing on the top could do it. Maybe make humans/aliens get hurt when they're on it, or just leave the gate to be stood on?
What about structures? Can people build structures on it/around it? For the aliens, should the dretch class be able to attack it, because in some servers the dretch isn't allowed to do damage on structures like the arm or the turret.