Unfortunately, the key challenge with the problem isn't architecting a DVCS-like service for legal documents (for an MVP, you could easily get by simply designing a novel frontend to git), it's an adoption problem. The current system is flawed, yes, but merely offering a superior product for less money isn't enough to make a dent in the bureaucratic nightmare of modern-day Washington.
I'm reminded of an article I saw here on HN a few months back: http://www.informationdiet.com/blog/read/dear-internet-its-n...