AbuseFilter should be able to filter by the content of all slots.
At present, filter variables that are backed by the ParserOutput will match all slots, since the ParserOutput objects exposed to AbuseFilter is the combiend output of all slots. In contrast, filter variables backed by the raw content (wikitext) apply only to the main slot.
As a baseline, AbuseFilter could simply concatenate the raw content as returned by Content::getTextForSearchIndex before initializing the variables. Ideally, AbuseFilter would allow filters to specify which slot the should apply to.