The downside of building in stuff is that you can't easily replace it. I don't have any VMS experience, but the versioned file systems I've studied are very far from being a replacement for what I would consider version control today. They're more like the automatic writing of backup files in Emacs.
Distributed FS sounds like something with a huge design space. It's better to do that in userspace. Was Plan 9 really the first time virtual file systems could be implemented in userspace? It seems like such an obviously useful idea in retrospect.
