We'll need to backport rpmkeys --list and --erase to pqrpm in RHEL 9 because we're not shipping the main rpm binary in there, and it'd be rather strange to have RHEL 9 pqrpm support something rhel-10 main rpm did not.
Besides, we want to drive people towards using rpmkeys to manage their keys anyhow because that's the right thing. So this actually serves two purposes.
This is not technically a requirement for PQ support though.