This is exactly my thought: I'm surprised an airline hasn't come out and said "Our goal is zero IDB and we think we can get incredibly close with a couple simple features in our app." An auction inside the app is the obvious/easy way to implement. I would think that would work on any of the Big 4 where app usage is at least sufficient enough to generate participation and meaningful bids.

Could even be a cost-saver for the airline: you might pick up a few people who *want* a couple extra hours and will put in low bids. Plus if miles were offered, I lot of FF'ers would happy play that game, which works out better for the airlines' books than gift cards/vouchers or obviously cash.

You could augment with a manual process involving gate agents (if app penetration is too low or for certain international markets), but my guess is that your typical domestic flight would attract sufficient bidders to avoid the IDBs just through the app.

There would be no need for rules about profession, status, etc. No caps needed.