If this interest you guys, you will most likely be interested by what we do over at prismic.io too. Basically, we're a service too, we output content as JSON too, and are very focused on versioning too; but we also have what we call the "writing-room", a very user-friendly UI to let non-technical content writers write comfortably without needing tech tools such as Git; and we come up with our own content query API.

It works with most technologies (we have kits in JS, Ruby, PHP, Java, Scala, Python, ...), and we did release a static website generator based on a JS engine which we called baked.js.

Check us out if you're interested in tech-flexible, design-flexible content management where content is nicely versioned.