Quick update to share, first spin of the main boards is nearly done, just need to run the I2C lines:
And a bit more detail around the microcontroller:
For those of you who are wondering, I'm going to try using one of the new AtTiny828 chips from Atmel for handling scanning the board and control of the LEDs in each key. The pair of 0805 pads you see to either side of the controller determine which side they are (right or left) and which address to use, meaning you could actually have 4 main boards connected at once
the same controller will be used for the thumbboards as well, because while it will be over kill, it'll also help keep pricing low and the code base similar.