It matters because as a Targaryen, he like Dany, is possibly impervious to fire. He may even end up as a rider of one her dragons. And in the line of succession, he would come after Dany to sit on the Iron Throne as he is her nephew and she can't bare children of her own.

Because it's significant that he's part Stark, part Targaryen. The latter means Jon has the blood of the dragon and Ned Stark really was an honorable man and was faithful to Catelyn Stark. With Jon, it's not so much important about how he plays the game of thrones but who he represents and how he came about as a…

Bran was thrown by Jamie in season one, at the very end of the first episode.

But maybe it was a plot by the Umbers to get rid of Ramsay and it failed. And perhaps they stil have a Plan B.