Yeah, I heard that one, and was equally skeptical. If they did get swallowed up by the crack, though, then they can be spat out by the crack again.
Maybe that's what the Pandorica is. A kind of netherworld, set apart from time and space. And maybe he destroys it in the finale when it's opened, creating a stable time loop? Because it gets sploded, it cracks time apart and the cracks fill the Pandorica with Cybermen and Angels and Rories, and because it's full of Cybermen and Angels and Rories it has to be sploded for the good of the universe, creating the cracks.
I don't know. I'm just speculating. I think it's a fairly Moffaty explanation, but it doesn't factor in the jacketty Doctor or the tardis exploding or any of that business. I'd say I'm possibly right, but I hope I'm wrong. I had the similar experience two years ago - my friend thought he'd come up with a solution in the week between The Stolen Earth and Journey's End and I thought "that's got a good chance of being right," and I was dreading having possibly found out the explanation ahead of time. But it was wrong and the next week was full of surprises. Thank god.