You know what is the mega-feature that is missing? Git integration. Yeah, it's geek, I know, but it would be a phenomenal way to publish a website (edit, commit, push).
Even better than git for publishing, I like the "fork" concept as applied to the more general web. Forget copyright issues for a moment... if you could fork sites here it would allow for really fast site creation where you can build off others' creations.
Ward Cunningham's Smallest Federated Wiki[1] is basically what you describe. To edit a wiki page you have to fork it into your own wiki, which I think automatically creates links and things. It's interesting but I haven't explored it nearly as much as I'm sure it deserves.
