There have quite a few discussions on the brush editor and why it needs to be improved from a UI standpoint.
Brush editor is too large.
Think about how to manage brush thumbnails better
Stacked brushes and adding more UI complexity
It is currently difficult to find and identify brush presets when you have more than 10-20. You cannot see their names, so you have to click around if that is what you are searching by. This becomes more evident with things like the pixel engine.
maybe other things to think about with this that I am not considering...