I think this could be the start of something amazing. A midi keyboard seems essential but if you could progressively introduce the different elements, using both hands, pressing enough keys to correspond to chords, different hand positions I think this could be a really great way to learn. If it could give feedback on being partially correct (e.g. highlighting two parts of the chord where you need to press 4 keys) it would be learning via gentle nudges, moving onto the next lesson once you're consisting getting it a new element correct.