I would pay a bit extra to have 30 minute's worth of 'horizontal time' in a small bunk for flights over 10 hours in duration. However I assume that because this

I would pay a bit extra to have 30 minute's worth of 'horizontal time' in a small bunk for flights over 10 hours in duration. However I assume that because this isn't a thing already, someone else thought of it, did the calculations and worked out it wouldn't be profitable for the airline.