How to use a UPDI programmer video: https://youtu.be/OVSLsA9-gF0
More information and firmware: https://github.com/ElTangas/jtag2updi
Getting started with the new ATtiny chips: http://www.technoblogy.com/show?2OCH
megaTinyCore: https://github.com/SpenceKonde/megaTinyCore
UPDI Programmer based on ATmega: https://easyeda.com/wagiminator/y-updi-programmer
Development board for ATtiny x14/x04 series: https://easyeda.com/wagiminator/attiny-814-development-board-smd
Development board for ATtiny x16/x06 series: https://easyeda.com/wagiminator/y-attiny3216-development-board-smd
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.