I have this idea of a 'hybrid GM mode'. All the players would be playing characters, but one would be the 'hybrid GM'. That player would still be playing, but perhaps while playing against, or with the other players depending on possible map types, he would have access to certain triggers on the map already predefined.
I think it could open up a strong type of storytelling. There would be this one character in the game who is an important figure to the story that the game wants to tell. By giving that power to the one special character, I think it would allow for some interesting gameplay. Letting a single bad guy act like the crazy summoner, that triggers a bunch of spawns while still in complete control of a character, aiming to kill off the heroes that wants to invade.
Or escort a VIP through hordes of enemies. The VIP character would have access to certain triggers that shows the power of this legendary person, something that will show and tell why this person was so powerful in the first place.
Maybe this idea in my head can be done if there is a possibility to make custom abilities instead, which I'm not sure will be in the game. Either way, being able to whack up the game is something I think it needs, more creative freedom when it comes to multiplayer and custom content.