Very interesting, thanks for sharing! I also have been involved in rhythm games creation, so I created a special editor for such type of games. You can try it on my page https://vfpe.itch.io/mboy-editor MBOY Editor. It's game agnostic and can be used for any game for so-called rhythm mapping. I added markers support, to make possible to attach specific game logic to the notes. You can apply it to your game if you want.