I got this idea while writing my article about the Adjustment Bureau, but I thought it deserved a post on its own.
In this game, we have two GMs, each one trying to guide the party to a separate goal. Perhaps the GMs are representing feuding Gods? Or, they are just an abstraction, with one GM trying to help the party achieve their goals, while the other one acts to prevent them.
Of course, there will need to be some sort of currency expressing what each GM can do, and how often. Perhaps each has control over one aspect of the setting?
Anyway, this is just a rough idea, which would need to be expanded and detailed a lot to turn into a proper game, but I think it could be a fun experience.