(disclaimer: Netlify employee)
(disclaimer: Netlify employee)
That said, it didn't help that you don't support Gitlab, which is where all my sites are, and which is the more important reason why I couldn't get it to work.
We (Graphia) took a similar approach for our document management system. Essentially it looks and acts like a regular CMS but it sits on top of a git repo instead of a database; and publishes via Hugo.
It's not intended to be a fully-fledged CMS but the API would support it without much work; the UI is definitely the time consuming portion.
http://www.graphia.co.uk for anyone who is interested, not quite ready for prime time just yet. Soon.
Feel free to ping me using the contact info in my profile or at @benaiah in our Gitter room (https://gitter.im/netlify/NetlifyCMS) if you're interested in discussing this elsewhere.