Imagine if we had a bunch of playable elementals factions for wind, fire, water and earth. Fire we would all dps spec and be hostile to everyone, water would include 2 healing specs and 2 dps. Earth would include 2 tank specs and 1 dps. For wind it would be 2 dps and one healer. The other specs are neutral to everyone, but can be hostile.
Or a demon faction with every playable demon available.