Finally got around to actually building a V4 Board and it works. *master* branch requires no modifications.
If you're building this board, note that you need the following:
- nRF52 Feather Express (nRF52832 *not nrf52840*)
- Install *version 0..8.6* of Adafruit nRF52 board lib for Arduino. Any later version contains API changes and a different bootloader version. So your best bet is 0.8.6.
*Reason for building a V4*
My previous V3 board worked flawlessly for 6 months and then decided to randomly start getting stuckkkkkkkkkkkkkkkkk keys. It was infrequent in the beginning, maybe once every 2 days but eventually turned into once every 2-3 hours. That's just unacceptable. I would clean the PCB and that works for a while but it comes back after a few days.
To make sure it isn't firmware related I decided to build a fresh board.