Guess no one else knows or has any need..
As you have observed, this has been requested by a number of people over the past several years; see this feature request in the official Adobe feedback forum: Unique Keyword Sets. You could add your vote and opinion to that topic to make it a little more likely Adobe will prioritize it (though they've made almost no changes to keywording over the years).
Meanwhile, if you're a good touch typist, you might try my Any Tag plugin, which makes it easier and faster to apply keywords (especially those containing spaces).
Not an answer to your question but-
Only a 'work-around' method for Keyword 'Sets' (>9)-
To apply a whole 'set' of keywords to other images- use one image with the 'set' of multiple keywords , and then copy and paste all the keywords into the Keywording panel of the other images.
Have several 'Master' images with different 'sets' of keywords.