Awesome work! I was planning on doing the exact same thing but looks like you beat me to it. It's great to see UPDI programmers in a small form-factor like this and I think they should be more widespread moving-forward as Microchip releases newer generations of modern AVR parts.

Thank you. The only problem with this UPDI programmer is that you have to solve the chicken and egg problem first ;-) In fact, I plan to use the new AVRs more often in my projects in the future, but I still have so many old ATtinys lying around.