Hey, everyone. Similar question here.
I used to use the rotary encoder on the logitech craft keyboard. It has an annoying overlay, but the zoom works so much nicer than mapping cmd+/- to some knob: It works in quick view and other odd places and doesn't necessarily have steps like keystrokes do, if your hardware allows it. It zooms where your mouse is not in the middle of the window and so on.
Please add this function if you haven't already.