If you treat the uuid as an opaque binary random value (which is how programs -should- treat it) then variances between versions, or custom versions, have no ef

If you treat the uuid as an opaque binary random value (which is how programs -should- treat it) then variances between versions, or custom versions, have no effect. As long as they gave sufficient randomness etc, from a program perspective they are unique id's. There are already multiple versions in active use (4, 7 and arguably 8) so you really shouldn't be using the uuid as anything but a long-random-value. Yes, the database engine may appreciate one version over another for performance reasons, but that's irrelevant to most developers and programs.