We’d be interested in something like this, although draw.io is slightly more complicated than our ideal - more wanted something like the shared equivalent of a whiteboard we can share ideas with, but still stored, and probably as versions.
Yes, I’ve tested it with both instances (https://draw.io) and with my local version of Draw.io.
You can specifiy the Draw.io App URL in the Admin Settings.
Doh, I just got mine working. The only thing I am stuck on was the custom mime type, since I don’t want it to open generic xml files. I also did 99% of mine in javascript using the remote draw.io server.