Think about that for a second though. One thing the GoT saga has in wild abundance is rightful heirs. There are like 22 of them in any given scene of the show, and I assume the books have just as many, if not more.
I'm kidding, of course, but considering how much of the plot is driven - and infinitely complicated - by the number of "legitimate" claims to the throne, isn't it reasonable to suppose the story might take such a turn? Technically Jon has taken the black and can't make any claims to the throne, even if he is a Targaryen. But the Night's Watch may well be toast shortly, and just as Jamie could easily have left the King's Guard, Jon may well be released from his oath and challenge Dany. Jon would have a legitimate claim both to the North and the Iron Throne, and he wouldn't need to marry anyone. I think the idea that Lyanna Stark and Rhaegar Targaryen might be Jon's parents is plausible, is all I'm saying.
And this is totally off the "Who's Jon's Mommy?" topic, but this is the second season in a row to start off completely ignoring how the previous season ended. At the end of Season 2, the White Walkers were literally marching on the wall, and then, nothing...or almost nothing...at the beginning of Season 3. At the end of Season 3, everyone is gathering their armies to defend the wall. But so far this season there has been bupkis about Walkers yet again. In the preview for this week's episode, there is a glimpse of a Walker, so maybe the trend will change, but I kind of doubt it. The show has been teasing about imminent attacks of Walkers since the opening scene of the entire series. If something doesn't happen pretty soon, that particular plot device is just gonna get boring. Like the boy who cried White Walker or something.
And this is off-topic too, but it just occurred to me: where the eff is Gendry? If he's still in that rowboat, he's dead by now.