[throwanem]

You're describing something not wholly unakin to sleeping racks aboard a naval vessel, although no doubt much more comfortable. They are more space-efficient than beds, but less so than seats.

In order to stack hammocks or racks three-high, transversely to the fuselage axis, as I suspect you intend, you need both a large amount of vertical space - eight or nine feet, minimum - and roughly a second row's worth of space between racks, in order for people to get into and out of them. The former requirement can be reduced at the cost of squeezing people unpleasantly together and potentially dismaying claustrophobes; the latter requirement can be eliminated at the same cost, plus that of exclusively end-on entry to and exit from the rack, two-thirds of the time via a ladder.

At this point the only customers you've got left are those fit enough to be physically able to use your service, and also unconcerned about being cheek by jowl with at least two strangers - or, if the racks have sidewalls, unconcerned about spending however many hours in a box too small to sit up in. A lounge might alleviate that concern, but what about the others? And where will people put their shoes? (Do you wear yours into bed?)

The alternative is to compromise space efficiency for comfort, and a lot of airlines already do substantially that with A380s and individual sleeper pods.