I think what you described is basically ownCloud Infinite Scale (ocis). I haven't tested it myself but it's something I've been considering. I run normal owncloud right now over nextcloud as it avoided a few hiccups that I had.
OCIS seems to have lost most of their team. They now work on a fork called OpenCloud. https://github.com/opencloud-eu
OCIS seems to have lost most of their team. They now work on a fork called OpenCloud. https://github.com/opencloud-eu