So when you replace tools' icons in GIMP's GTK3 branch with symbolic ones that +Barbara Muraus
and +Jakub Steiner
did last year, this is what it looks like. The are plenty more icons ready to replace the old ones, I just haven't used them.
Some icons are still missing (newer tools, selection add mode etc.), and most, if not all icons are finetuned for 16×16px size, so they are not pixel crisp in 22×22px size. But that still looks infinitely better to me.