It doesn't require long runways. It's taxiways that are the problem. The A380 can land or take off anwhere a 747 can land or take off. The problem is that in some cases all other aircraft movements at an airport might have to be stopped in order for "the One" move around the airport.
The problem is that in some cases all other aircraft movements at an airport might have to be stopped in order for "the One" move around the airport.
Something quite like that is probably already in place for security reasons.