I know I should have read more but it was late at night!
I was thinking of using one of the 'quad rail' dual humbuckers. so you have a sensor, a driver and a hum canceling pickup all in one unit. would the hum cancelling not efffect the EM output of the driver?
but as you've said that'd probably mean re-winding one of the coils to make a driver (I've thought aboue making some pickups anyway so why not start now!)
I guess this would still have the oscilation problem of the driver and sensor being to close. I'm sure they's an electronic way arround that (some modification of a 90 degree phaser to make a 180 degree unit that would cancel the oscilation?) but that'd just make things more and more complicated.
I had a thought about the problems with single notes and chords: as long as you were playing something that wasn't dischordant shouldn't all the notes frequencies be harmonics (I know that's the wrong term but I can't rememeber the right word)?
guess I'll have to go back to the drawingboard!