And who will the three dragon riders be. I think the two may be connected. I wonder if Arya is a means for Jon to end up meeting Daenerys. At some point he is going to be a dragon rider since he is half Targaryen. Maybe Bran will be the other if he can mind-meld with the dragon.
Others say Tyrion might be (half)-Targaryen too (Tywin: "You're no son of mine" and another potential rider, although I still see him more on the advisory side of things.
You mustn't be afraid to dream a little bigger, darling.