@Suspicious_Actions Have you looked into Qubes-remote-support - New features and support for Whonix 16 - #3 by Insurgo ? (It’s testing users members only for posting though)
A lot simpler then your design, but maybe some of the ideas there could be reused?
What I would be looking for, personally, would be reusing all the glue there to have hidden-onion setup and ssh redirection to dom0/admin-vm, with console session sharing. Having that would permit a user to start a remote admin session, share the shared secret by its own mean to remote admin, and land on a shared terminal. Then everything typed there would be seen by both parties, where at any moment the user can end the remote session. Of course, limiting access to that shared tty would be needed, but to me that would be the missing feature of qubes-remote-support, since have shared GUI access through tor is having a lot of latency. Where needed for some use case, most of the needed work still needs to be done from dom0/admin-vm.
Thoughts?