A paper piano might not be that unrealistic
This YouTube video of a paper piano is meant to be a joke, but when you think about it, it’s not really that far off base. You could imagine a vision-equipped computer watching what you’ve drawn, recognizing that it’s a piano keyboard, and looking for “keypresses.” Each time they occur, it could play an appropriate note. Likewise, you coud conceive of a Tablet app, where someone could draw a piano on the screen, recognize it, and play along as the virtual keys are tapped.