I can't see this actually getting anywhere for the simple reason that the planes will have space that potentially isn't being used on some flights, which I can't see the bean counters being very happy about, 200 euro or not (happy to be proved wrong here).
If the space was convertible back into seats then I can see the sense, but not if there will be Y seats empty because pax have decided to pay the extra for a bunk. What happens if you can't get to sleep, despite trying counting Sheep etc. do you have a seat you can go back to if you want or not?
If loads of people pony up the 200 euro, and there are lots of economy rows empty at the back of the plane, those pax who didn't want to fork out, can just lie across those empty seats.