I'm not sure if this would be useful for any other scenarios or if it's doable, but I had an idea that would possibly be useful for a scenario in my rig.
I am using the expression pedal in most situations as a mix control for the wet signal on my Nemesis delay. I mostly keep the mix pretty low, but the expression allows me to quickly and easily change the effect level.
I had the idea that allowing a second message to engage when the pedal is a specified point through its range would be useful. For example (and how I would use it), at the halfway point of the exp pedal range (increasing the mix of the delay), the feedback control would kick in on the expression pedal as well and increase, so as I pushed the delay mix higher, at a certain point it would also increase feedback and lead into oscillation.
I know I could have it change both levels now, but I wouldn't want the feedback to diminish at the minimum level, or even to increase unless I pushed it above a certain point.
Again - I haven't thought through if there are other applications where it would be helpful or not, so it may not be a desirable or useful feature for many. Just a thought. :)
(Edit - just thought of another useful scenario... as you increase the gain on a drive pedal, at a certain point, you may want the treble response to decrease simultaneously, but not throughout the entire range of the pedal.)