there seems to be an opportunity for designing a new kind of forum to facilitate this sort of collaborative work. perhaps the traditional threaded model of forums like HN, phpbb, and others isn't optimal for this sort of collaboration.
Perhaps the Wave protocol could be adapted to this sort of purpose. It seems designed for it, really.
There's already a LaTeX bot called watexy.
This seems quite similar to the question "Is open source software viable?"
Except that in open source software there are well known ways for splitting up work. In mathematics... thats not really the case (or at least, not to the same degree).