There are many variants of the aircraft being proposed, the most capacious (extended capacity, single class) allowing for about 840 pax.
The A380 will probably be aimed at the busy inter-hub routes to allow for consolidation in market growth, however there's still, at the moment, a limit to the number of people that want tickets for a given flight.
"Is an airline really going to give up 200 revenue passengers, inexchage for installing a half-a-million dollars of gym equipment and plasma screens?"
Airbus currently meets with interested airlines once a month to discuss progress and future developments. Indeed, airline specification shaped the aircraft from the start. A project worth £6.7 billion .. It's in the manufacturer's best interest to think of these things
Economy class is being designed with improved space, that's correct, and in the same way business and first get their own enhancements, including partitions and other additions.
Areas underneath stairs where pax would be unhappy to sit are being considered for small bar areas.
The A380 has a range of about 14500km.. So anyway, without the "MegaCrap" features to which you refer, how much will you enjoy your 18 hour flight? (It's in the airline's best interest to think of these things too...
)
Regards,
Andy