What a very creative alternative layout for your QFR. I particularly like the index placement of brackets at Y's original place.
Where is your tilde and backtick key ("~ `") ?
I use Colemak on OS side, along with a couple of custom layers. Here, it's backslash with AltGr or Fn or something.
I wish I have an ErgoDox but I'm afraid there's no switching back from this nonconforming setup.
Dunno, I swap all those keyboard around along with a typematrix and my thinkpad, and it's fine.
On your ErgoDox, there are so many Ctrl keys, which one (or a few) do you use most?
I usually use the unix-like (home row pinkie) or the thumb-cluster position, depending on other keys in the chord. The corner keys rarely get any usage these days, but they're still there for *some* chords like Ctrl-Alt-Delete.
And have your developed any "thumb pain" using ErgoDox?
Not really. I did feel some strain, when I also used a thumb to click on a trackball a lot, though. Furthermore, I'd strongly prefer vertical thumb cluster, but that's about it.