This sounds cool. We wrote a git-based CMS[0] that is a little different. It has a nice-enough UI for creating and editing markdown documents, which are stored in git. And then it has a JSON API so that your main site can fetch the content and style / format however it likes. Users log in with OAuth or local passwords and their edits end up as git commits that are attributed to them.
[0]: https://github.com/frameable/junco-cms