ONGOING! Prototype stage of analog synth sequencer driven by an arduino mega (for the analog I/O, sure multiplex is also possible) that controls XR2206 synth parameters via vactrols and AD5206 digital pot. The nixie display is by https://hackaday.io/robotbugs
and is SPI as well as the pot. 4 channels. 1: base frequency 2: waveshape 3: bandpass (on square output with phase inversion) 4: filtered square/sine-triangle cross mix.
Nixies indicate beat clock divider, backlighting follows envelope parameter for each channel.
3D printer has come in handy with this; the vactrols and mounting hardware specifically.