For a wheel to stick out on the top would mean a bulge sticking out of the laptop, and I don’t think that would fit the current aesthetics of the aluminum chassis.
Shameless plug:
Honestly, I’d say it’s crude at the moment, but there are ways that it can be improved later on. Currently, I have not found any rotary encoders that would fit within 2mm (in height) while sporting a knob wheel, so it’s not possible fit it in a standard expansion card form.