I think with the new Merc/Sellsword rework and the possibility of introducing other neutral classes, that it might be good to have the following change:
Total number of “random BD” goes from 7-9 to 6-8. Total number of non-killer neutrals goes up to 2-4. However, Mercenary (or Inquisitor, in Sorcerer games) becomes guaranteed. If, in the future, there are other neutral classes that are BD-friendly (not necessarily BD aligned), they may replace Mercenary/Inquisitor as the guaranteed “good” neutral (just like the game guarantees Alchemist/Physician).
I think this is an overall neutral change for Unseen/Cult (it adds one more unconvertible class, but it reduces overall BD numbers, also more room for Sellsword), a slight buff to Neutral Killer (one more person that pings Neutral to investigation) and a slight nerf to BD (one less confirmed BD, more incentive to rely on Neutrals, but one guaranteed BD-friendly Neutral makes up for it).
I think it would be a good change, overall.