I checked open-scsi and followed the instructions given by chewitt in the thread open-iscsi support for raspberry Pi 3. Creating an image with Iscsi-client worked but I don't have a scsi drive. Maybe it would work, maybe not.
Then I checked nbd-client, which is built into LibreElec:
- export the dvd drive on my Ubuntu server unsing nbd-server
- the nbd-client command on LibreElec to connect the drive returns with no error
- mounting /dev/nbd0 fails with various error messages (dmesg)
Now I made another test and installed ndb-client on my Xubuntu laptop
- connecting the remote drive works
- mounting /dev/nbd0 works (type seems to be udf, which looks ok)
- the disk can be played flawlessly with VLC as if it was in a local drive
Looks good so far, but changing the disk is not recognized and has weird effects on the mount.
Conclusion: Even if nbd-client and mounting the remote drive would work on LibreElec, this will never work like a local drive. In my opinion, it's not worth following up beacuse there are even more problems to be expected...
Maybe someone has more and better ideas.