Since GitHub is starting to feel Emacs-like, why not go fully in this direction? Add a "dotfile" repository for everyone to manage their own client-side JavaScript extensions for Github that would be loaded by default. And then let people collaborate, share and create extensions and "configurations". Want a better map? Fork the official one and modify it. And then let others fork from you.
This would make scripting attacks really hard to defend against. They could use something along the lines of Caja, but it's a really hard problem in general (and one they're worrying about, given the gh-pages move to a separate domain)
