AFAIK, one of the basic design criteria is that the plane can use existing runways and park in the (maximum) space allotted in the typical airport layout. Getting 800 pax on or off the plane is going to be a bit of a challenge, but it’s basically speaking a question of more jetways glued on to the terminals. It’s not as if 800 is several orders of magnitude bigger than 400.
The lines at the INS counters is going to be something to see, though… 
S. Norman