Would anyone like to be among 800 passengers on the sasme plane? How long would it take to get off and on, never mind getting luggage? They would have to offer a lot of extras to First and business-class passengers.
It's bad enough being on a full 747.
As I understand it, part of the gate modifications for the A380 include 3 jetways for loading/unloading, so that's only 260 per jetway, a normal load.
Same for the baggage area, a fully loaded A380 is like having two 747s arriving at the same time. You will just have to have several carousels for the different class passengers.
Several US airports have already begun the modifications necessary for the A380.
However, I don't think there will ever be enough destinations to justify a fleet of 500 A380s in the world.