[ownedbycats]

The AO3 adapter collects "comments" (though I am not sure whether it's user comments or something else), so its just a matter of putting it somewhere:

[archiveofourown.org]

## Some adapters collect additional meta information beyond the
## standard ones.  They need to be defined in extra_valid_entries to
## tell the rest of the FanFicFare system about them.  They can be
## used in include_subject_tags, titlepage_entries,
## extra_titlepage_entries, logpage_entries, extra_logpage_entries,
## and include_in_* config items.  You can also add additional entries
## here to build up composite metadata entries.
## archiveofourown.org, for example, fills genre (a standard
## entry) as the composite offreeformtags, ao3categories in
## include_in_genre.  If there's ever more than 4 series, add
## series04,series04Url etc.
extra_valid_entries:fandoms, freeformtags, freefromtags,
 ao3categories, comments, chapterslashtotal, chapterstotal, kudos,
 hits, bookmarks, collections, byline, bookmarked, bookmarktags,
 bookmarksummary, bookmarkprivate, bookmarkrec, restricted, series00,
 series01, series02, series03, series00Url, series01Url, series02Url,
 series03Url, series00HTML, series01HTML, series02HTML, series03HTML

You can try this:

[archiveofourown.org]

## adds to titlepage_entries instead of replacing it.
extra_titlepage_entries: comments