I would love to have a visual representation of the 'value' of my volume pedal. At least when moving it.
The problem it would solve for me is that I quite often use the volume pedal to fade out or mute the guitar when playing in a band. Then when it's time to 're-enter', it's hard to know how loud I will be. It would be nice to get a visual clue (0-127, a % or a segmented bar) so I could quickly restore the volume to the level I know would be fine even when I'm not playing.
This could be implemented for all expression inputs by only showing it when one of them is moving.