In terms of regulation, wouldn't it make more economic and comfort sense to enable sleeper-only flights where everyone lies down, ala Japanese capsule hotels? Tight spaces are much more comfortable when I'm lying down than when I'm sitting.
These used to exist (and still do on some flights). I flew on Singapore Airlines from LAX to SIN when they still had their Airbus A340-500 flying nonstop in about 18 hours between Singapore and Newark or Los Angeles. The whole plane was just 100 seats, business, lie-flat only. Frankly with the odd wide seating they have, you could have easily put 140-150 in there.
Doesn't even need to be sleeper-only flights. Just book business class on pretty much any international flight. (Which is actually much more comfortable than seat configurations for most of the time the Concorde was flying--much less the Concorde itself which was rather cramped.)
