I see that pqv: links statements to qualifier value nodes, but it doesn't return anything for item-valued qualifiers [e.g.]. I am using qualifier hashes in Wikibase-cli commands, and I'm having to get the JSON for each statement from the database and extract the qualifier hash from there. In thousands-long batches, those database calls take a lot of extra time; it would help a lot if I could just get the hashes in my sparql query. Thanks!
Topic on Talk:Wikibase/Indexing/RDF Dump Format
Indeed, in the RDF representation complex value nodes are meaningful only for values that describe something where extra information is useful (units, calendars). Because other wikidata items can be described unequivocally with their ID they do not need a complex value node attached to them. We do not store them because they don't add any value to the graph and would probably increase the number of triples quite significantly.
My understanding is that qualifier hashes are very much internal to the wikibase entity representation and you should not assume that the RDF model is using them, in fact it does not seem to use them for values (it does for references). So I would strongly suggest not using WDQS to track such low-level information.