Lie-flat seats in business class, are a fact of life. Even private cabins and showers are now a fact of life on airplanes. I have traveled on bunk beds in economy style class train cabins for >22 hours trips in China. Every time I travel on cramped economy class long-haul journey, I wonder why this concept isn't implemented in the airline industry?
Wouldn't it allow the same number of travelers, but with a lot more comfort?
I can imagine there are safety concerns, but is it really more complicated to get out of a bunk bed than a 10 across or even 11 across row in case of an emergency?