Ok, this idea has been in and out of my mind for a while...we've all talked about apps and whatnot, but what about a checkbox of some sort: "In exchange for a 5% discount at the time of booking I agree to be bumped to a later flight arriving at my destination within four hours of my originally-scheduled arrival time."

I've actually pondered whether a ticket which does not come with a seat on a specific flight (or flight pair) but instead simply guarantees travel from A to B on a given day (or within a time range) at the airline's discretion (so long as the airline informs you of the flight times...say, 48 hours in advance) in exchange for a discounted up-front price would be a winner? Basically "You'll travel on Monday but you're agreeing that we can put you on whatever flight set has the lowest load factors".