Agreed. It is atleast a metric that can be tweaked as opposed to pretending that all packages with inactive upstreams is a deep resource drain on Fedora.
I would suggest that when we identify such packages, we take steps to try and get more maintainers for those packages first before trying to cull them off. For instance, sending a note to fedora announce list and here with the list of problematic packages. That way, everyone will have a fair chance to try and rescue the packages they care about.