Writing a proper Android version is currently tying for first place with a micro.blog (http://micro.blog) client for my next project.
Should you really be interested in a Linux version, Quiver's author has written up the json format: https://github.com/HappenApps/Quiver/wiki/Quiver-Data-Format. It seems simple and sane.
I also like the general notion of "Standard Notes" (https://standardnotes.org/), but can't see text-only notes becoming 'standard' in the 21st century.