Looks cool! I wonder how you'd negotiate authentication with this... both users logged in presumably, you could record edit author as whoever clicked the save button (or upon each action in a "real time" saving application).
Both people are accessing the website as themselves. If one person doesn't have permission to see a page, for instance, then they won't see it. And yeah, whoever hits save is the saver ;) Doing something richer than that requires application-specific integration, which we want to support, but we also want to take cues from developers about what that should actually look like. This is one idea we have along these lines: https://github.com/mozilla/togetherjs/issues/372
