This is both very cool and eerily reminiscent of MVFS and ClearCase. It's a huge change in Git, going from de-centralized to hyper-centralized. If I read it right, git status, git commit and even running a build or cat'ing a file may not work if your network or the central server is down.
I hope they have thought hard about how to get the "Git proxy" for remote sites working well. If they end up with remote sites working on a 15 min - 1 hour old tree that will be very annoying.
Do you know this, or are you speculating?