The 380 represents an interesting problem. The seat mile cost is great - but only if all the seats are full. Start having empties and your per seat mile costs are now going up.
With yield management the response is sell the seats cheap - below "cost" (cost is a very elastic term). This is only a short term fix - and leads to a public expectation that if I hold out I can get it cheap. In some respects yield management has become the tail that wagged the dog.
In the US the reponse has being many airlines found it was cheaper to go to a smaller plane and "dump" the cheap seats at the back.
Interestingly the profitable airlines - jet blue - south west - dare I say Ryanair - and other LCC's have all gone the route of smaller planes - high frequency.
What happens on the long haul international market is different - but the 777 has cut into the 747 sales.
Another area often overlooked is the actual cash generated off a flight - First and Business are basically paying the way for the whole plane. Offered an option I suspect these passengers will avoid a mega bus with more chances for delays.
These two trends are obvious out of Newark - 15 years ago you got on 747 and went to London and then went to Belfast, manchester etc etc. Now you can fly direct - every night to Birmingham, Glasgow, Manchester, Shannon - all on twin jets.
The even more interesting trend is Lufthansa is now running all business class 737-800's to dusseldorf every night - 48 seats @ $5,000 RT - not a bad deal. I believe they have expanded this service.
So depending on the trends the A-380 may become a sink - lots of churning - little profit. If it can maintain loads and the right mix it will be a cash cow. The one buyer who does not have to worry is FEDEX.
One thing I do know is you can forget the waterfalls - gyms - food courts - etc - great hype - the beancounters will jam in the seats.