My $.02: I think getting players involved in writing scenes makes sense (that's actually my plan for an upcoming group game, which I do plan to make episodic and to structure after an action television show). Anything above that I'd be dubious about: the role of the GM came about because trying to spread around responsibility for the game -- how the world works, where the story is going, how to implement the rules -- to more than one or two people is generally not practical. GM'ing does take a lot of time and energy and it's not for everyone, but I think the idea that the work can be offloaded on the players, no matter how much goodwill they have or how talented they might be, is fallacious. Without someone who's agreed upon as the game's authority, groups larger than two people will naturally tend to pull apart because there's no means of resolving disputes when they come up.
This is unless you're effectively playing a card or board game with roleplaying "fluff" added, in which case the GM-less game could work.