This one's a cracker ...
But, as is often the case, it is only a Patent and may never get bought by the carriers:
Airbus, the plane manufacturer, has patented a mezzanine seating design that piles passengers on top of one another. In this design, passengers are able to recline into a lying position, but the seats are also stacked on top of one another, so that another set of passengers can fit just a few feet above the first.
Economy class is about to get a lot worse | Business News | News | The Independent