Thanks a ton!
I think we've arrived at the limit of how I understand the daemon to work, and GUIX_DAEMON_SOCKET. I think I understand that you are using a single node (hpc of sort I imagine), where users create sessions, and within which you provide the guix command, having set up GUIX_DAEMON_SOCKET to a unix-domain socket (to that same node / itself). That makes total sense in the context of the single node. Did I get that right?
I think what we are aiming for, in our case (where users each have their own nodes as it were, only sharing network drives), is providing the guix command on each node, set up with GUIX_DAEMON_SOCKET connecting with ssh to a master node with a daemon, that itself would have access to the same network drives.
The issue with profiles you are mentioning is interesting; I haven't quite thought it through yet. I think I would personally want users to be able to create profiles (for reproducibility reasons) but I guess it would work the same way with guix shells built from manifests, maybe slightly less easy to interact with, I don't know.
Etienne