Very elegant in implementation and looks fantastic as well. What are the dimensions of the PCB? Were you able to decode the addressing in order to use a single SCSCI ID for both functions?
PCB is 80x100mm. There's a technical discussion with a bit more detail here:
Just FYI to those who are building this: The BOM has a discrepancy (at least the CSV BOM on github does) where it calls for an atxmega64, while the firmware is built for atxmega128 in the makefile. I don't know if it will make a difference, but I would assume the 128 is the correct part.
I ordered the atxmega64 from the BOM without checking, and it would program but wouldn't boot up. After a few minutes of head scratching/debugging, I realized I had the incorrect part. I changed the target AVR type in the makefile, so we'll see if it works with the ATxmega64 once I have some time to set it up.
Also, to program this chip you'll need a PDI programmer, I used my EEPROM programmer TNM5000, which does support PDI (and writing the config EEPROM) over the ISP port. I think you may also be able to use a buspirate and avrdude, or JTAG.