As a fan of vim putting escape on the home key was probably the first thing i did, swapping caps lock for escape is common amongst vimmers.
Using the emoji layout to get an easy thumb layer idea is a good one On my ergodox, 2 of my big thumb keys would swap layers. I liked having the right hand side turn into a number pad, and whilst the numbers are very reachable on the blade, that's still a thing I miss. Similar to you, I don't use the abomination of qwerty, so I'd need to take the time to reprogram it to Colemak. And kill every emoji off the thing too. Ick! It makes me sad that this site turns my perfectly nice little textual emoticon up there into an image, but a keyboard full of em? There aren't enough forks to stick in my eyes to deal with that!
I've not actually done much layout editing though. As I'm in the UK I've made £ easily available. I don't want to fiddle with the symbol mapping too much so that the green legends will be valid reminders, and a UK mapping changes a few things there. So I keep it as US and have the £ symbol as shift and $, which works for me, oh and € on the top row. Also with (most?) European layouts, the left & right Alt keys do different things, and due to the chording needed to do Alt, this means there are certain combinations I can't do which are handy for some bits of software I need to use from time to time, so I've got Alt+R on the function layer when I press my R. That's about it for me for now.
I use this thing all day as a professional software developer, and I think that it's a testament to how well designed the textblade is there is so little that I want to change with it.