This whole thread is very interesting.
However, the major issue is that many proposed changes require redesign of the PCB and case.
Does anyone willing to take the job?
As for angled or flat design, I have 3 ergodoxes in use now, one with the original design, with 2x thumb keys, the second one is the one with angled thumb cluster, the "frankendox", and the third one is a 80 key variant of the original, with the 2x thumb keys replaced by 2 1x keys.
I have to say, these are all not optimal, but I can live with them. So far I prefer the angled design, but it is more complicate to make than the flat design.
I have no idea what the optimal design would be, however, at least to me, the major issue is not the thumb cluster, but the pinky finger.
======= below has nothing to do with thumb cluster, you can just ignore them =======
The problem is that with the current layout (qwerty), my left pinky is too heavily loaded. There are two approaches to solve my problem, one is to redesign the layout, but I would need some to retrain my finger and this would be a long process. I don't have time for the time being. The second means is to adjust the staggering of the pinky column, because I use the '1', 'q', 'a', 'z' keys a lot, yet to reach '1' and 'q', the left pinky finger need larger movements. Thus lower the pinky column can shorten the moving distance of the pinky. However, this require the redesign of the PCB, which is beyond my ability now.