I don't think they'll do that. Your mobile order doesn't take the place of/prevent someone else from using the ordering system. When you cancel, it simply makes it such that the next order prepared will come out a little bit sooner. With ILL, your "order" takes a spot for a finite amount of time and does not reduce the wait time for the next paid rider (they are already scheduled for a set time); TWDC can't easily resell your spot last minute and hence will miss out on that revenue.
Now, allowing you to cancel up to an hour or so prior to your scheduled ride might work, but unless guests complain frequently and loudly about not being able to cancel ILL reservations I doubt they'll change anything. They already covered their....behinds... in the disclaimer.