Lots of effects boxes have knobs that could be useful to adjust during a performance, but it's awkward to do so if you're already using both hands to play the guitar. Some let you connect an external pedal, but that means interfacing with the circuitry of the effect.
Instead, let's have a pedal with a long Bowden cable (or whatever the right term is for one that transmits rotational force) that you can screw onto the shaft of a pot instead of the knob that's usually there. Alternately, the fancy version has a regular (optical) pedal and a servo, so you can control the knob via a radio link or MIDI. The latter would be useful for automation too.