MIT already has aircraft designs that use 50% less fuel per seat-mile. If more of the plane is empty there is higher incentive to reduce seat mile cost especially if average seat mile revenue is lower.
Can you show me a ref to this design? (And yes, I tried to find it myself.)
I suspect it doesn't actually work for the simple reason that fuel is the number 1 expense of airlines, and a 50% reduction would be utterly enormous for them - if such a thing existed it would be in extremely high demand.
Mind you that the company still receives the money regardless, the only change is that they have to enforce the contract (not the other way around). Here in Germany, you would probably mandate them to charge your bank account directly and that is almost, if not impossible to get out of.
A very possible outcome I see here is that you would probably be given a window in which to checkin, which will no longer hold until 2 hours before the flight, so they can sell the seats that were not claimed a second time
