TiddlyWiki[1], which is a wiki more than a "CMS", has been doing something very close to this for quite some time. I used it for years, but eventually switched back to plain text files for notes.
I use Jekyll for blogging and generating my portfolio site too, but right now I can only update my those from my own laptop with my Jekyll install which is not always great. CMS.js would be something else... My dream would be a simple PHP based CMS for my Jekyll install though.