The customisable top row makes me so happy. Just a couple of minor tweaks I'd love to see: custom labels, preferably smaller text and also maybe button shapes? Even if the hit area may be the same, actually seeing button shapes makes me just a little more confident in hitting the right button.
E.g. the labels for "clear blending mode" and "clear (canvas or selection)" are "CLE" in both cases. With custom labels I could find another combination that makes sense and lets me tell them apart.