over in the Smacked Upside the Head with a Guitar thread, which I just now noticed (having just gotten back from a trip,) Michael (anonymouse) raised the idea of swapping/reversing the GM/player roles: one Player, multiple GMs. Mike Holmes raised the valid point that players might not be thrilled with that suggestion, since being the GM usually means more work. if there is only one protagonist player and multiple GMs, everyone will be clamoring to be the protagonist.

another approach might be to have one protagonist per "subplot" or "character arc", with each player acting as a GM for one character arc. some time ago, I started a usenet thread about GMless roleplaying that included some ideas on how to do this. I thought I'd excerpt a few of these ideas here and open the thread for brainstorming on making somethink like this work. one footnote: I mention in this thread a game called Fungeon, just as an example of a GMless game, which I then suggest some modifications to create an RPG with a plot/arc (what I refer to as "auteur gaming" in the thread.)

I wrote:
suppose you have an elf mage, a dwarf fighter, and a human paladin in a
typical fantasy world, and these three plots:



• the slow death of the elven race
(why are they disappearing?
what can be done to save them?)
• racial tensions between the empire and the dwarven kings
(can an alliance be forged?
will it break down into war?)
• the machinations of an evil high priest
(can he be stopped?)

I wrote:
one GM per scene: this is prepped pretty much the same way as one GM per session, but the play will probably be more cinematic, with scene cutting, party splits, and so on. this could be handled by planning the main floorplan of an adventure area as a group and assigning sections to each GM, who can then place a couple secret rooms in the unmapped areas. who gets to be GM is determined by which area of the map the characters are in, although there may be an overlap; some connecting passages or rooms may be designated "neutral" and will be empty except for when the characters are chased/followed from a controlled area. thus, you can have a ruined elven village (plot #1) with a secret encampment of trolls in the western section who are stirring up trouble between dwarves and humans (plot #2) and a still-intact temple in the center that has been taken over by agents of the high priest (plot #3).

another approach, based on Fungeon or another random map technique, would be to divvy up duties each scene. take an example where whoever creates the treasure/traps for a scene is different from whoever creates/plays the enemy. suppose the player assigned to create the enemy for the current room is creating the dwarf plot, while the player assigned to create a treasure is creating the elf plot. the enemy player might create an evil dwarf who might not attack immediately, but might say something like "what, have you finished burning the dwarf outpost already?" then notice that he doesn't recognize the party and shout "WHO ARE YOU? guards! guards!" and then four goblins run in to defend him. when the battle is over, the player creating the treasure describes any treasure/trap and includes a scroll in dwarvish reporting what a dwarven patrol discovered in an abandoned elven village.

I wrote:
one random approach would be for each player to write on a series of cards different roles or plot elements. for example, the player playing the paladin wants to battle an evil cult with secret members engaged in some nefarious plan. in this method, the paladin's player is responsible for the paladin plot, but details aren't worked out. the player writes, one per card: High Priest, 1st Acolyte, 2nd Acolyte, Servant, Sacrificial Victim, Demonic Minion, Slave, Ritual of Summoning, Assassination Attempt, Evil Alliance... in other words, roles and events that might occur in an "evil high priest" plot. at the beginning of every scene, the players would roll to see who gets to play one of these cards. suppose it's a tavern scene, and the dwarf, elf, and paladin have arrived on a rainy night. there are the usual rough-looking tavern types, a monk in black robes, a woman with an ornate composite bow. the paladin player wins a die roll, and draws a card: Servant. the player can now suggest that someone in the tavern is a servant of the cult. depending on what ground rules the group set up at the beginning of play, this may mean the player gets to say "the amazon-looking woman is really a Servant of the high priest!" or may mean that one of the characters is a servant, but the paladin does not know which one; whoever is playing a peripheral PC in the scene could choose to make that character a servant or the decision might be made by a die roll.

You might be interested in checking out WTF? - The game of competitive storytelling. In particular, there is a brief collection of optional systems and rules at the bottom of the page that could help out with some playmodes. The "executive producer" (where multiple directors verge from a single core director's storyline) and "writer" (where there is one director who must somehow incorporate whatever plot elements are introduced by the writers) options seem most up your alley.