@TopazRabbit @davidrevoy I'd love to see your progress. I did a macropad for Linux for myself on the cheap. I use it daily and it is magical!
https://github.com/poleguy/remap
I also use a work provided huion Kamvas pro 13 for remote whiteboard type engineering work (krita mostly). Pen works fine but I never bothered configuring the buttons on it.
@poleguy @davidrevoy Here's what I have so far. No public plans available yet, but I'll get around to it eventually. Uses QMK for config and has hot swappable sockets for the keys.