I actually have a related question for you, @Pyteo … how did you generate the thumbnails for these brushes? Was it a manual process or were you able to automate it in some way?
I was considering updating thumbnails for some of my other favorite brushes to use this more “Photoshop-ey” style. I quite prefer it!
Just wondering if you had any tricks or tips! I took a crack at doing it manually, but.. your icons are all so consistent and nice-looking 
(I was hoping Krita would have a way to automate this, but apparently not yet. Though there is a feature request that’s been open for some time!)