I'm about to watch "The Doctor's Wife". I'm excited to see it. My long-term long shot guess: River is Amy's mom (remember, Amy grew up with her aunt and uncle). The kid is Amy. Amy is half Time Lord.

This explains how they got out of the paradox when the Tardis blew up. It explains how Rory-the-robot remembered Amy. Amy is a fixed point in time, because she causes herself to be born.

The Doctor already said that the whole saga is about what makes Amy special, and why the Tardis found her in particular.

Also, Rose Tyler will be back, because Bad Wolf is not over yet. (It "can't" be, because Rose touched all of space and time)