This is an idea I had many years ago.
Two players would be the normal co-op guys (2 master chiefs or Elites, whatever).
The rest of the players spawn as enemies that normally spawn in campaign levels. For example, you know in Assault of the Control Room, there's one bridge part where Grunts and an Energy Sword wielding Elite rush out of the doorway. The Elite would be a human player. He would have the same health/speed/abilities as the normally AI controlled character (cannot pick up weapons, grenades).
At another part there are Ghosts, Jackals, Wraiths. Human players will spawn as them too.
Once the co-op guys kill their adversaries, the CAMPAIGN CHARACTER players respawn at a later part of the level among other AI controlled troops, and wait for the co-op dudes to reach them.
It goes on and on like this.
Should the CAMPAIGN CHARACTER selection be random or selective?
Opinions?