Hi there,
i came from the same direction as @donnib. What @tyborall said sounded like a nice solution. Later I found this tutorial to install hassio incl. the supervisor on a debian system (supervisor, because i didn’t want to miss out on add-ons) Installing Home Assistant Supervised on a Raspberry Pi with Debian 11
the first hurdle was that dockers overlay2 file system is not compatible with NFS, so I created a iSCSI target on the synology and mounted it to dockers overlay folder. That worked. flawlessly. But now when the supervisor docker image starts it seems to reset the network, thus killing its own (iSCSI) and its host (NFS) root file system 
I’m not sure if this network reset is necessary or even intended, but as far as i can see the supervisor is a docker contained running with priviledged rights, and it looks liek it comes with its own init system as the entrypoint. I’m not deep into this but i wouldn’t be suprised if that has all kind of funky effects including a reset of the networking system…
@donnib did you find a nice solution in the meanwhile?
@tyborall do you have a supervisor running in the setup you described above?
edit: from here i see 3 options:
- give up on the supervisor and addon support
- try to build a supervisor image from a debian based base image (just because i would feel more “at home” there andcould potentially debug the issue)
- try to make the official raspi sd image bootable over network (though @tyborall mentioned some update issues…?)