What I propose is taking a pair of split coil humcancelling pickup--whether standard P style or a humcancelling J style--and rewiring them so that the bridge coil that senses the lowest strings is connected either in series or parallel with the neck coil that senses the highest strings. In effect, this would be similar to "flipping" a P bass pickup to even out the fundamental. The converse alignment of coils might be interesting, but probably would sound too disparate to be useful. Has anyone done something like this to achieve a reverse P bass tone with say a pair of DiMarzio Ultrajazz pickups?
I have not. John Kallas offers this type of switching on a quad-coil (humbucker type) pickup on a model he makes called the Jazzmaster. Pretty cool, IMO.
i think i remember trying this once with a pair of dimarzio ultra or area J split coil J pickups. amusing but mostly useless, it just sounded like the high strings were on a different pickup than the low strings. the tonal change when playing low to high was kind of distracting and unmusical. i think one of the goals for good bass tone is evenness, where all the notes low to high sound right within the mix. splitting up the pickups like that had the opposite effect for me.