David w/ the Participatory Politics Foundation here, we created & ran OpenCongress from 2007-2013, and now it lives with the Sunlight Foundation. I wrote about version control for legislation here on OC Blog in May 2012: http://goo.gl/Ll2rDs. I still think it's possible on a site like OpenCongress or GovTrack, it's possible on GitHub, and this non-profit is working on it directly w/ their MADISON platform for text annotation: http://opengovfoundation.org.