Open a Wii Nunchuck and solder a small 9-DoF board, a gyroscope, accelerometer and magnetometer, to its own I2C wires, so that its cable carries the turning of the hand and a fused 3D orientation beside the joystick, buttons and accelerometer.

Build a BNO086 orientation sensor and a small RP2040 board into a Wii Nunchuck in place of its cable: the sensor on SPI, the Nunchuck on an I2C bus of its own, and one USB-C port that is a serial port for OSC, a MIDI device, a gamepad and a mouse at once.

Build one battery-powered RP2040 base that takes Wii, USB, touch and analog controls apart and puts them back together as new instruments, with sound, a servo, LEDs and a small display.

Tape strip, force and fabric sensors onto an electric guitar to find which parts of it can be reached while playing the strings, then glue down the ones that work.