How about "QSL by Bureau?" and "QSL Manager Callsign" fields in Callsign Database?
Sorry, I know this forum is for suggestions for the logbook, but I couldn't find a comparable forum for the callsign database.
Ops often don't indicate in their callsign database profiles whether they respond to Bureau cards or not. Having a QSL by Bureau field like the QSL by mail/eQSL/LoTW fields might encourage folks to indicate one way or the other.
Also, I wouldn't mind a separate field for "QSL Manager Callsign" that hotlinks to the QSL manager's profile. Folks sometimes put their QSL manager's callsign in the QSL Info field, but it just gets jumbled up with other information. I'd love to be able to feed the QSL manager's callsign into my logging program and then search/sort on *just* the QSL manager's callsign.