I vaguely remember Airbus studying such an idea in the 1990s.
funfly is right to point out that the sleeping part would be great. The other parts of the experience less so. The economics only add up if the sleeper passengers are allocated a miserable economy seat for takeoff and landing. Add to that the climbing or crawling to get into the bunk doesn't square with most premium pax ideas of luxury. And since they wouldn't want to climb up to use the economy lavs in their jimjams, downstairs facilities would be needed. The list goes on. "Return to your allocated seats and fasten your seatbelts" ??
I don't blame Airbus, they have a knack of using outside partners to float ideas at very little cost.