It really needs an accordion soft-synth, and when you change direction (and/or when you start to slow down?), to play the next note in the song... as you said,

It really needs an accordion soft-synth, and when you change direction (and/or when you start to slow down?), to play the next note in the song... as you said, with volume depending on movement speed (and maybe current position also affecting the sound a little). In short, what we need is an VST to javascript bridge haha. And then make a litte plugin out of it, so this can be put on all websites; using a canonical CDN location would even mean everybody has it cached all the time, so there'd be no downside to doing that. I have been wondering what the web 3.0 would look like for a while now, but I asked the wrong question.... what does it sound like, that is what matters.