I love that piano like chorded keyboard (https://en.wikipedia.org/wiki/Chorded_keyboard#/media/File:X...) from the alto. I think it's still and interesting UI concept but I think it should/could be adapted to a foot pedal design, chords would be constrained to 2 inputs though unless maybe two of the inuputs were directly side by side then you could expand to three. Organists know what's up ;)