That "Bran planned it all along" theory would be even less satisfying than what we got, incredibly enough. This guy whose powers are never explained but apparently have no real limits and can see the future, planned everything off-screen with his omniscience in a world where everyone else is a mundane. And then he ends up king, without any of his motivations explained either. Woohoo. How exciting and deep. It'd be an extremely retarded thing to write, but there might some truth to it, because that could be the way GRRM is going, but obviously with boatloads of more exposition and challenge, etc., and D&D just took that small part of GRRM's ending ("Bran becomes king.")
More likely, though, is that it really is as simple as it looks. That's how D&D writing has ALWAYS been. There is nothing below the surface. When Bran says "why do you think I came all this way?" it's just him appearing mysterious and knowledgeable, saying he knew they'd choose him, which is why he bothered to make the trip. And that's it.
