I'm surprised Github integration isn't on their own roadmap. It would be killer to mark things as completed via commits and see code activity in one application.
We've already added support to pull in your commit log to your Overview feed (see: http://cl.ly/2r2K3N052j0G3w2G2i2O - you can enable this via your roadmap's settings page) and we're now looking at pulling in individual commit messages and posting them to roads as update messages, etc (like you suggested).
We're just now trying to decide on the best way to do this :)
