I'm fairly sure Elm was ripped out and replaced with TS later on.

Yeah, not sure if this is the same but here's a tweet about some recent tech usage https://twitter.com/AbletonDev/status/1143880805317525506

"Running on Web Audio, WebAssembly and WebGL. Made with three.js, Tone.js, anime.js and React using TypeScript and much "

That tweet is about the newer learningmusic.ableton.com. Apparently a different project, different stack.