Actually, imho meta-commentary does not work best in the summary. That is, while I agree with your basic idea that they should have a) canonical tags (identifiable and searchable as such) and b) non-canonical tags, being neither, I don't think the summary field is the best place to dump the latter; many summaries make little enough sense as it is. Perhaps a separate field?

My pet peeve is reader-assigned tags. Having one's work tagged "Mary-Sue" for the crime of including a sixty-something woman OC with incipient rheumatism in it and having nothing whatsoever one can do to disavow this nonsense has caused severe damage to my dental work in the past.