I get what you're saying, and that would be a pretty neat new mod destination.
Funny thing is, even though delay is not a mod destination, there is a CC number (#42) directly assigned to VCA Env Delay. Unfortunately, the Pro 3 can't send CC#42 to itself. But if you have something that can send selectable controller data (a DAW, or a QuNexus (that's what I'm going to try with), or various other things), you can at least play around with the idea.