The best way to understand what GRRM wants to do with King Bran is to think about it in mythical terms. Bran's will ascend to the throne as the new Summer King of Westeros, in the Oak (Summer) King / Holly (Winter) King sense. Funny thing - our story began with a summer oak king figure on the throne - King Robert - and even the "First King" of Westeros was a summer oak king figure. Bran will not only help to end the new Long Night, but to make sure the dream of spring gives birth to summer.