Everyone can submit their own update of RFC 3454 to the IETF and advocate for their proposal. I don't care strongly which solution is chosen, if there is a good migration plan to the new idea. Meanwhile, implementors will route around the damage and pick their own solutions.
OK, let's suppose just for the moment, that we decide to have Stringprep point to version 24 or higher of UAX #15. Can you think of a migration plan that would satisfy ultra-conservative implementors like yourself?
The spec could suggest that all problem sequences are to be rejected.
Erik