I support this idea. I've been wanting and alien gamemode in which you have two teams: The Colonial Marines and the Aliens. The Colonial Marines start with some custom made weapons that are identical to the ones from the movies and there is one alien at start, the queen. The queen lays eggs that, after time will hatch to NPC facehuggers that roam and hug faces. After some time that horribly unlucky marine wakes back up and can go about their busines until being killed by the alien planted inside and they gain control of the alien. After awhile, they molt and become a regular alien. The Marines win by killing the queen/all aliens/blowing up wherever they are and aliens win by infecting all marines/killing all marines/infecting X amount of people.
BONUS: There could be a third team, civilians. They are basically marines with lower health and less powerful weaponry.