Obra, I was wondering why you'd only put 4 thumb keys on the keyboard and not 5?
See:
Those 2 extra keys on the thumb "row" are easily reached* and it would be so cool to have an extra layer key, or any kind of key, on that row.
* If we take a regular keyboard for instance, a touch typist can still comfortably reach the left Alt key using his left thumb. The left Alt key, compared to the modified Model 01 image above, is even farther away from the thumb without leaving the home row. Similarly, the Ergodox has only four comfortable thumb keys, you can see that they're almost as far away from the thumb as the alt key of a regular keyboard:
My question is, what was your reasoning against putting that extra key? There's plenty of space, looks like it would perfectly fit in there...
I hope it wasn't because of aesthetics or that the number of keys had to be a exponentiation with base 2.