Ability to use the mouse-wheel to scroll through your quickbar (1 to 10).
Could be a key to toggle mouse wheel between scrolling and zooming, like, middle mouse button (when not aiming at an inventory, as it is "sort inventory" in that case).
OR
Simply make all 4 (scroll quickbar left/right, zoom in/out) freely configurable in the options/controls so everyone can do what they want like shift-scrollwheel or whatever.