By the way, about "multiple metadata is not supported", there are already multiple links for the same block device in /dev/disk/by-id, e.g.
ata-HTS721060G9AT00_MPC3B2Y3GK0S3E-part1 -> sda1
scsi-SATA_HTS721060G9AT00_MPC3B2Y3GK0S3E-part1 -> sda1
Why not just do that in /dev/disk/by-uuid when you are not sure about the type and UUID of a block device?
By the way, about "multiple metadata is not supported", there are already multiple links for the same block device in /dev/disk/by-id, e.g. AT00_MPC3B2Y3GK 0S3E-part1 -> sda1 HTS721060G9AT00 _MPC3B2Y3GK0S3E -part1 -> sda1
ata-HTS721060G9
scsi-SATA_
Why not just do that in /dev/disk/by-uuid when you are not sure about the type and UUID of a block device?