Bunk beds in aircraft cabins: the realistic prospects

Bunks in airline cabins harken back to the glamorous, glory days of flying, the long flights where your white-gloved flying butler would show you to your sleeping quarters and draw the curtains of the flying cocoon before you emerged, hours later, at either your destination or at an exotic stopover. 18-hour-plus flights are the new normal now, with the definitions of long-haul and ultra-long haul stretching ever longer. So is it time to revisit the idea of bunks?