Actually.. - not sure if I am going anywhere by this, but hey.
You know these "Choose your own Adventure"-type of books? How about making one of those then?
Edit - As will become obvious, I quite dearly loved them as a kid. I think bay12 would be a great place to make one of these together, no?
Each "GM" can write one "turn" per, well, turn. That way, there won't be a "First! Reserved" roadblock, nor would anyone be able to "monopolize" the story.
Brainstorming for Rules:
-Set a Limit on each "Branch" - like 3. We don't want to fight the dragon in 5 different ways.
-Open-Climax writing? The GM's don't know the success of their action, which is rolled by the thread-gm, and added with a single paragraph
(That way, we can have failure, and a set of circumstances)
-Right. Circumstances. Finding that steel sword, gives a +2 on the D10 combat roll. Or thereabouts. Just let us hope we can hold on to it long enough, to actually make a dent in the adventure
-Minimum Limit on turns for possible success - just that we won't escape the "situation" within 3 or 4 "turns".
-Maximum Limit on turns - each story-point, branches off into 3 new ones. A hydra-situation indeed. Each turn after the, oh.. 6th?, will take a culuminative -3 roll-result. Or something along these lines - Mainly a sudden death mechanic, as to not explore "too widely" into the adventure.
-Getting-Ahead limit - We don't want anyone rushing to the goal all too quickly. How about you can't write a continuation for single-branch-continuation? That way, to advance, we "have" to write different choices into those turns, that we want to advance.
In essence, safe for the first turn (3 choices), we thereafter (9+ min) have an ever increasing number of "story-telling spots".
By having a "random" system rolled by the "True" GM, it will have an interesting twist for the story-tellers
Everyone can "in", and while it is possible to reserve 1/3 of a specific story-spot, the overal story can be written by anyone intending to do so.
If it does go well, we could even make a "short story book" out of it, with a number of "better explored" good and bad-ended routes for display (and dead-end routes discarded).
(Heck, that would be great fun. The "True GM", could afterwards create the "story" thread, take the two-digit number of turns that made it into the final version, jumble them around safe for the first post, and then take the reader for a good ol' spin with html-hotlinking by the turn-bottoms.)