Which means someone would have to sue someone else... and if I understand @pemerton correctly, Wizards is almost certainly the only one who could bring such a suit. 3PPs have no way to force the issue -- not individually, and not collectively either.Sadly, that would have to happen in court.
So it's up to WotC to decide when or if "de-authorization" is put to the test. They could wait years until there's a target worth going after. They could never file suit at all, and just hold the threat over the heads of 3PPs.