I'm working on a project called http://makeyourlaws.org. It's open source and non profit. Simply put, it's a practical project that aims to completely replace existing legislatures with online liquid democracies, through incremental steps within the existing legal system that have real teeth all the way. No waiting for a revolution and no begging. Read the site & its G+ page for details.
In particular having a git for laws is going to be a necessary backend system — along with e.g. pretty diff, blame, mass import, in-browser editor, simple markup language for laws, etc.
MYL is not git-based as it were — the policy authoring process is discussion- and voting-based, as it's a fundamentally different process than code authoring — but once it does get to being about laws, git is a good model.
There are of course also a number of other subprojects within MYL, like legal identity verification, empathy-creating discussion systems, factchecking, privacy-preserving voter-verifiable auditable-in-aggregate cryptographic vote proofs, etc etc.
If you're interested in working on git-law, or online liquid democracy in general, please contact me either by email to makeyourlaws@saizai.com or posting a comment at https://plus.google.com/100183759660923071401/posts/NQVuM65j...
We're making it happen.