ZFS should let the user specify or modify the fsid_guid of a dataset
The fsid_guid of a dataset is used to derive the vfs_fsid when the dataset is mounted. It is then used as the fh3_fsid if the filesystem is NFS exported.
The ability to modify the fsid_guid, or to choose it for a newly created dataset, would ease the migration of NFS clients from a NFS fileserver to another. (if the fh3_fsid is the same on source and destination, no umount/mount is needed on the client)