Solution I suggested is to add new "in-readtbl" form in addition to "in-readtable". And lock *readtable-alist* from changes somehow. I
it's been a long time i've seen such kludgery being suggested...
don't know how we implement locking *readtable-alist* without patching named-readtables. Patching named-readtables is out of our authority, but I believe we need to consider it (maybe apply a patch) if we want that the entire system would work well.
just make a fork of both repos, record the needed changes in them, and when it all works and is tested then start nagging the maintainers to include your patches.
there's no need for any kind of authority, just working code of a reasonable quality (note: i'm pretty sure anything like the above mentioned kludgery will be rejected).