Dude, this is so cool! I've had something like this floating around my cluttered headspace for ages, and it always sort of floats to the surface during the rare times when I do some light sysadmin work via Termux on my phone.

Another thing that jumps to mind is the minichord[1], a nominally open-source synth/instrument.

I just love seeing these little devices people can come up with given the proliferation of the necessary devboards and tools. Nice project.