Instead I'll answer you here: There's no theoretical maximum - you can build an airport large enough to accommodate basically anything (though it might require moving to a dry lake bed in Nevada), and demolish/rebuild/retrofit terminals to service it.
I'm assuming that, with current engine efficiency, there's going to be a limit where you can't push a large object through the atmosphere and have it be going fast enough to generate lift.
And that's assuming you could build a stable wing of that size to begin with...
But you'd likely have more space... I always thought you could, with the advances in windows materials, maybe build some really big windows into the front of the wing too.
That way we could actually see where we are going.
I got it from this Scottish guy in San Fran a while back...haven't figured out how to actually make the molecules bond properly, but when I get it... look out.
The Hangar
The Hangar