Mad idea, maybe, but I was just thinking...
Overnight trains in mainland Europe have six-seat compartments (three facing three) which at night can fold out into six bunks... might we see something like that one day on long-haul planes? Yes, I know there are issues of lower ceilings, and g-loadings, and seat belts... but it wouldn't take up an awful lot more space than ordinary seats...why not?
(Remember, you heard it here first!
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