Hmm, very cool project and maybe just the inspiration I need.

I bought a Baby Einstein Magic Touch Guitar for a friend’s daughter a couple of years ago, and while it was okay as a toy, it was disappointing as a musical instrument because the chords it plays are badly chosen. It’s basically impossible to play along with most songs.

I’ve had the back burnered idea to buy another and improve it; maybe I will now, following a variation on your approach.