User blog comment:Dragonzzilla/ME3 Multiplayer DLC I Ideas/@comment-5020449-20120430014302/@comment-4967682-20120430021944

Still, it's very likely that the Collectors will be added eventually, considering the MP team has toyed with the idea of adding new enemies, and the Collectors were supposed to be in the game in the first place. Not to mention that they're the only faction that makes sense.

I imagine in such a situation, Harbinger (or his stand-in, like "Collector Biotic Troop") would be a lot stronger in both attack power and durability, Assassins would actually stay at long range and occasionally toss a Warp, Guardians, Scions, and Praetorians would stay more or less the same, and Drones would gain a rifle butt melee attack, the ability to sidestep, and frag grenades (the Assassins and Guardians would get the same abilities obviously, except maybe the grenades). The pure number of ways the Collectors can knock players out of cover (literally every unit except the Assassin and maybe the Guardian has a way) would force players to adapt and work together.