I love the trivial yet effective circuitry of an electric guitar or bass. That sweet spot of usefulness and simplicity pretty much defines my aesthetic sense for all things!
The basic guitar circuit has just a few elements, all 1930s technology:
There are many possible combinations of these simple elements, and many possible embellishments.
So anyway, I had a dream last night of a circuit I think might be surprisingly useful while still being very simple. I imagined this circuit for a 2-pickup guitar like a Telecaster or Les Paul, but I bet it could be adapted for guitars with 3 pickups, or a single 2-coil pickup, or whatever.
With this circuit, the player can blend the 2 pickups in any combination, e.g. bridge alone, neck alone, both at full volume, neck at full volume and bridge at half, et c.
Furthermore, the player can reverse the blend by throwing the volume control switch — if volume 1 is on 10 and volume 2 is on 0, it’s a traditional pickup selector. But it could also change the sound from neck volume 10 + bridge volume 5 → neck volume 5 + bridge volume 10, or other pickup blends.
For visual cleanliness and (I think) playability, the volume control switch should be packaged together with volume 1 in a push-push pot.
As an embellishment, you can imagine additional switches to change the 2 pickups to be in series or parallel, or to coil-tap the pickups, and so on. You could also use the switch in a push-push pot to take that pot in or out of the circuit. The extreme form of the idea would be for all 3 pots to have a push-push switch, and use each switch for something.