Actually, its very simple. For a mod that you want humans vs. humans, just skin the alien side as humans, with the human structure. So, the game says its aliens, but in reality its just humans that are tagged as alien team. Of course, im not sure the whole upgrade and turret system will work on the team that is marked as aliens.
Of course, a simple solution would be to edit the maps so the "alien" side has usable armories and turrets already on the map.. but even then problems would happen.
Anyways, i would rather not have a Human vs. Human game, it kinda defeates the purpose. Play tribes or another game if you want to do that.
However, a "catch the dretch" gamemode would be awsome. No bases, but its everyone vs. a single dretch, that has the ability to wall-jump and wall-walk, double health, and is alittle faster. Actually, what would be better is that the speed and health of the dretch depends on how many people are playing. If only 2-3, the health boost and speed boost would not be noticable, but if your against a full server of 20 people, then you could have a health boost as big as x5 and same with speed boost.
No spawns, so the dretches goal is to last either 10-20 minutes, depending on the players, or kill all the humans. If the dretch waits it out however, he might be in trouble. Every 3-6 minutes (depending on players playing), the humans reach the next stage. So, you might be super-dretch, fighting against S3 if you dont hurry up and kill.
You could also have it so whoever kills the dretch "evolves" into the dretch, and the previous dretch "evolves" into a standard human. So its kinda like Gun Tag, except you can kill the players. If this version of the mode is introduced, have it so the humans can spawn though. Then, the player who is the dretch by the end of the time limit is the winner.
That sounds more like an apropreate alternative Tremulous game-mode
