Having been watching humanity for about twenty-one years now, I can say the declaration of a capitol city will have to involve something stupendously inane and self-destructive... I'd say that we'll probably hollow out Earth's core for a wonderful, 'centralized location' sentiment, all the while failing to even consider the effects this would have on the planet. Ironically, I think the capitol city would, in its construction, become the only habitable city on the planet.
You know what? I'm going to buy up development rights to the core, so that if someone is silly enough to suggest a city down there, I'll get to play the role of the surly, old squatter. Is it bad that I generate ambitions based strictly on what will piss people off later on?