My Eventide H9 would display a 0-100 number on the screen as you were adjusting the expression pedal and it was incredibly useful. I use my expression pedals for reverb and delay all the time. When I want a wet sound it is nice to know I'm at 75% of expression rather than %55 which on some pedals is virtually the same position. The indicator should show when you move the volume or expression pedal and hide a second after the change is made.
Make it happen! 