While the app is an interesting idea, I really think that at the end of the day it's only going to be a signal for "how many people are interested". As others have noted, there are many incentives that someone might be up for on a short delay versus a long delay.

I do think the idea raised elsewhere of tying compensation to delay time beyond "just" the four-hour limit has merit. If the IDB rate were 16x/$5400 for a 24-hour delay versus 4x/$1350 for a 4-hour delay, UA would probably have considered either (1) offering to put the pax on the next flight to SDF (and potentially confront an overbooking situation at the gate there) or (2) put them on another airline. Doing this would also "put some stick about" playing games in low-frequency markets.