Btrfs already has separate fsid and device id. Anyway, if you clone the device then those also stay the same, so I'm not sure what this would solve. How would the complete solution look like?

AFAIK the filesystem UUID, the device UUID, or both are sprinkled all around the filesystem, I suppose for reasons of identifying data belonging to the fs in case of fsck. According to my quick research device id cannot be changed. I suppose if it could be changed by some means, then btrfs rescue clear-uuid-tree could be used to fix the other uuids.