I think thats indeed a problem with a Terminator-verse, if there are more factions then definately. An Alien versus Predator versus Terminator verse might be interesting though. Kind of like the best of three worlds.
Plus the background material would be interesting:
*Alien, Aliens, Alien 3 and Alien Resurrection
*Predator, Predator 2, Predator Concrete Jungle
*AvP Movie 1, AvP Requiem, AvP game 1, 2 and Extinction
*Terminator 1, 2, 3 the coming 4 along with Sarah Connor Chronicles.
Also there are the books and comics to consider as all. I think there was a Terminator hybrid that made use of Alien biology, some infiltrator units etc etc.