At the moment package_update_index_rpm() in package_rpm.bbclass uses MULTILIB_PREFIX_LIST which is set up in separate mostly duplicated anonymous python code in rootfs_rpm.bbclass and populate_sdk_rpm.bbclass. package_ipk.bbclass uses ALL_MULTILIB_PACKAGE_ARCHS for the same purpose; surely we only need one variable for this. Some refactoring needs to be done to avoid the apparent duplication in code and variables, ensuring that all users (including the package-index meta-recipe) remain working.
MULTILIB_PREFIX_LIST was eliminated with Laurentiu's refactor, so I'm marking this as fixed.