Oh dude, I love this. I've been working on an interactive music thingy (https://trebel.la, it's sort of gamified but more designed to structure practice sessions for serious classical musicians) and struggling with the ABC vs. MusicXML choice.
Like most people in the space I'm using ABC for LLM generation (e.g. generating sightreading exercises and etudes) but MusicXML for processing and rendering the output. Would be nice to have something somewhere in between the over-simplified ABC and overly verbose MusicXML.