I must sadly announce that I have found a flaw in the PCBs.
The PCBs were supposed to allow one-unit keys in the outer columns (switches 2:0 to 5:0 and 2:13 to 5:13), but the upper holes for the switch pins are somewhat misplaced, making this difficult.
You
could cram a switch down there, but one of the pins would be bent in a weird way. You would also need to use a modified plate because there are no holes for any switch mounting pins, and there are important traces on the PCB where you would have drilled them.
If there will be an ErgoDox version 2, I suggest that this flaw be fixed. Also that each trace going to a diodes is moved somewhat so that one could drill for a mounting hole without breaking the trace.
...
I had in a previous post promised to post a couple of ideas I had for bridging the gap between the thumb-keys and the main keys.
In the image on the left, I have used a 2×1 Space key (one that I had previously made from a thick row-A numpad-0) on the key below M. It does however nudge against the N key, so some of the Space key would have to be cut off. I also found that offsetting the outer thumb-key made it easier to reach.
In the image on the right I have cut a Space Bar to size with the stem offset inside the key. Here, I used the middle PBT space bar from a Cherry G81 keyboard. If I had used a regular Space Bar for MX keys, I could have used the end of it and at least one end would not have been open like this one it on both ends. (I just did not have any MX space bar that I was willing to sacrifice)