I've pondered the idea of a moderated Wiki, where edits come in more-or-less as patchsets which the owner can apply or not apply. This was a while ago, and I'd say my idea is totally trumped by hosting Wikis on git, such that changes really are patchsets, complete with a massive infrastructure to support dealing with patchsets. Wrap a decent web UI around the basic idea, enhancing the git workflow to better support the idea of "submitting" a patch out of the blue, and you might have something powerful. I believe such projects are in progress.
(For git, substitute your choice of DVCS.)
The point of this being that if you pick and choose patches deliberately, with of course the opportunity to modify them as you go, then you can end up with something collaborative that still has a strong editorial voice. That might be something new. It'd have to be very open and easy to use to work at all, but it might.
You can create a repository to collaborate a post with your friends. Whenever you want to publish the post, just push it to the http://yourname.github.com repository.
(For git, substitute your choice of DVCS.)
The point of this being that if you pick and choose patches deliberately, with of course the opportunity to modify them as you go, then you can end up with something collaborative that still has a strong editorial voice. That might be something new. It'd have to be very open and easy to use to work at all, but it might.