I'd be interested in setting up my 8-string with separate outputs for each pickup just to see how it sounded.
I currently run through an ABY pedal going from A to my bass amp (set for normal 4 string use) and then from B to a small guitar combo with the bottom end rolled right off and then a bit of dirt and reverb added. This gives some great shimmer and grind without muddying the bottom end.
Being able to send the neck pickup to the bass amp and the bridge to the guitar amp might sound very cool........ or might not sound much different at all and so be a waste of time.
There's only one way to find out, and i've got enough on my plate that it'll probably never happen. 
I currently run through an ABY pedal going from A to my bass amp (set for normal 4 string use) and then from B to a small guitar combo with the bottom end rolled right off and then a bit of dirt and reverb added. This gives some great shimmer and grind without muddying the bottom end.
Being able to send the neck pickup to the bass amp and the bridge to the guitar amp might sound very cool........ or might not sound much different at all and so be a waste of time.
There's only one way to find out, and i've got enough on my plate that it'll probably never happen.