Would this not be useful? Seems like most of the old Gibson guitars had a passive tone knob for each pickup, but I don't remember seeing any current basses with that same setup. Seems like being able to roll the treble off of only one pickup instead of both would yeild a lot of useful tones. Roll the neck pickup tone all the way down for some thud and blend in a bit of snap from the full up bridge pickup to put an edge on it, no? Has this setup been tried and generally found useless? Will the cap from one pickup pull down the tone from the other when the pickups are blended? If that's the case, is there a way to isolate the pickups with a couple diodes or something? Could that be made to work for series and parallel modes?