It reminds me of systems in the "Sustainiac" family for generating unlimited sustain in an electric guitar, at any volume. There is a powered circuit which drives feedback into the string through a coil ("reverse pickup"). Typically the reverse pickup is in the neck position. So effectively the vibrating string becomes part of an oscillator circuit.
We can imagine a harp like instrument (or koto) with multiple steel strings, oscillating under a Sustainiac-like pickup feeedback system, and used as the basis for synthesis.
It looks as if the reeds in the Korg instrument might work similarly.
This video is nice because it talks about the feel of the Sustainiac: how it "kicks in" and you feel the vibration swell just when you fret a note with your left hand.
https://www.youtube.com/watch?v=hsbdvkIua8o
This one does a good job of demoing the three way harmonic switch:
https://www.youtube.com/watch?v=LZwPPGsxY6g
You can sustain the fundamental, or have it go to the octave harmonic, or even a higher harmonic above that.