Thanks for posting this! I've been experimenting with adding generative ambient music to my white noise app Ambiphone [0] using tone.js, but I've just been using manually written progressions and motifs, so I'm really excited to try this out.
Just a heads up that your example at https://observablehq.com/@ricardomatias/playa doesn't seem to be working at the moment because of browser autoplay restrictions - the console errors that look relevant are:
> An AudioContext was prevented from starting automatically. It must be created or resumed after a user gesture on the page.
> The AudioContext is "suspended". Invoke Tone.start() from a user action to start the audio.