If you don't like the SHOULD we can try a MAY without IETF consensus:
"An approved standards track RFC identified to specify 'patented'
technology after its approval, where contributors neglected their
duties to disclose IPR under BCP 79, MAY be removed from standards
track, if there's no IETF consensus for a different approach."
There is already a "default" rule how to get rid of cruft, but it's
not appropriate for such submarine patents, and getting a consensus
to demote the RFC might be tricky. With an explicit MAY the IETF
consensus has to be 'no, we want to keep this RFC anyway' to avoid
the demotion, and picking this "option" (MAY) would be limited to
the IESG (or the outcome of an appeal).