What would happen if ... to raise revenue among other things ... airlines gave reservations for and charged for overhead bin space? After all, airlines do (or did) charge for drinks and headsets.

Due to space irregularities, only some of the bin space would be reservable. For example the airline might start with just the bin spaces just behind each bin divider. If that panned out, it would be increased to the bin spaces just behind and just in front of each bin divider. The rest of the space would be free for all as is the case today.

Your baggage would ahve to be size legal, and that would make it possible to at least partially predict how much space it would take up.

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