I've long regarded the guitar as a proto-2D piano, because whereas the piano keyboard is linear, one-dimensional, the guitar fretboard has cells arranged in 2D. However, on the guitar, one hand has to pluck the string whereas the other shapes the chords. On the piano, of course, it's enough to press the keys, so both hands are used to play notes.
So I was wondering what a true 2D piano would look like, one where both right and left hands would play notes. Turns out the answer has been with us since the late 70s, when Eddie Van Halen introduced tapping. But the full realization of it came yesterday when HC showed me some YouTube vids of contemporary (and young) musicians. Check out ZackKim and weep!