This is just a quick log to mention that I have finally ordered the PCBs so I can actually test the design :)

Previously I have also verified that it is possible to run the ESP32 port of Grbl on the Adafruit Huzzah32 Feather, which means it should be fairly easy to use that Feather with this FeatherWing. I think it should also be possible to use original AVR Grbl code meant for Arduinos with the AVR Feathers.