I think that having each author provide a set of keywords to their CPAN module (very much like researchers provide for the articles they submit to journals) and having search.cpan.org have access to these would probably solve your problem. As it is, I would find such a tool useful. The only caveat would be that you would have to trust that the author of the module would provide enough relevant keywords to make the search useful.

metadoktor

"The doktor is in."