I think this repoman check should be made fatal to make it harder for people to ignore it. I cannot think of any valid reason for leaving an USE flag description in metadata.xml if it is not used in any ebuilds. QA team: Please sign-off on this and re-assign to the portage team for implementation.
+1
This is in the master branch: https://gitweb.gentoo.org/proj/portage.git/commit/?id=863001bddadccacda55b26adfa960ac5002cef71
Released in repoman-2.3.2