Would love to see a demo of this being used, perhaps with a camera feed of the keyboard alongside a screen capture of emacs - kind of like some of the typing demos by contemporary keyboard enthusiasts[0].

Personally I've been happy with GNU Typist (AKA gtypist)[1] because it's slim, cross-platform, doesn't depend on a browser, and is simple to extend.

[0] https://youtu.be/pXT89jnAz7k

[1] https://www.gnu.org/savannah-checkouts/gnu/gtypist/gtypist.h...