Very interesting input @Offray,
Rethinking all this half a year after the initial post, the backend-question is more in my scope - because (correct me if I am wrong!) interaction has to happen on a server.
I have installed yunohost and was happy to see how easy it is there to set up cryptpad, etherpad and other things I would like to iframe in TW excalidraw.
Specially regarding the implementation of TW in yunohost there is work to do to make use of the authentication features it provides. But I think this could be a basis to allow to host such a setup without being a genius.