The reality is, as I wrote in a previous thread, that the “user.*” class of extended attributes doesn’t have a success story to tell for almost two decades.
The information in the CommonExtendedAttributes page linked in the top post is very old and outdated. The fact it even mentions “Beagle” signals its antiquity. It should probably have a warning “THE INFORMATION ON THIS PAGE IS OBSOLETE.” to avoid wasting everyone’s time on a dead end.
It didn’t gain traction at the time where filesystem-based metadata was a cool new thing. So, let’s be real: it won’t gain traction now.