I think we should keep the fsf and osi tags. Both organizations are very important players in the FLOSS community and do far more than just maintaining and defending their definitions.
Further, I am against the tags free-software and open-source because they are too general. Per definition of this site, any on-topic question would be tagged with these tags. ...
Let's keep derivative-works and make the other two synonyms.
It is the clearest and searchable out of the three. The other two can still function as redirects. If something gets tagged with a synonym, the master tag gets shown anyway.
Since no one on the site has the 1250 reputation required to suggest a tag synonym (And no one would have for at least a few more days).
Your best bet would be to flag for moderator attention, and hope that one of the Community Managers see it.
Looks like the managers hath heard our prayers.
The topics of compatibility and incompatiblity of GPLv2 and GPLv3 and the difference of licensing under GPLv2-only or GPLv2-or-later are possible.
But I'm not sure if they are relevant enough to warrant individual tags for each license version.
We should not go ahead with this renaming. "dual-licensing" is the commonly used term and the term "multi-licensing" should have mariginal or no use in the context of free software.
The tag excerpt cited by the OP is IMHO incomplete and somewhat misleading. In the context of free software "dual-licensing" is a much used business-model that is common enough ...