IMHO, Zevon will be inducted eventually. It is only a matter of time.
Given the previous inductions of Joan Baez, Bonnie Raitt and Dr. John - The qualifications of at least one easily recognizable, iconic song coupled with being a favorite of music critics - the aforementioned precedents have already been set. And i say this as a huge fan of Zevon's work/catalog. He was a genius.