As you previously pointed out, mounting kernel filesystem requires special rights, so FUSE is just a dumb idea to (partially) work around them… I don’t really know if it can work!!! For instance, if the MinIO module mounts a FUSE/SMB filesystem, the final effect is to have SMB as backup destination.
So FUSE could ease the backup in the sense that it can extend the MinIO module (not the NS8 Core) capabilities.
About S3 protocol, it is widespread among cloud providers and also applications (like MinIO). And, most important, it is supported by Restic which is the NS8 Core backup engine.