So the man himself has apparently revealed hints about the final season of Game of Thrones. Reportedly George R.R. Martin has put clues to the final season of Game of Thrones in his latest book.
Apparently, it turns out Daenerys Targaryen is not indestructible after all. And her vulnerability increases in the cold. Well she is the mother of Dragons after all. Apparently, as per the book, Princess Daenerys the First died of "the Shivers," a disease that kills its host via the coldest conditions imaginable despite the presence of dragon blood. And until her death, the Targaryens believed that they could not get sick.
George R.R. Martin has also detailed a few abilities for Drogon and Rhaegal, who are assumed to be Winterfell-bound. Apparently, long before Dany, Queen Alysanne Targaryen, aka Good Queen Alysanne, queen consort of her brother, King Jaehaerys I Targaryen, wrote a letter describing what happened when her dragon, Silverwing, came face-to-face with the Wall during a visit to the Night's Watch.
The letter apparently details how Silverwing was scared and refused to take her where she wanted to go. Imagine that, a dragon scared.
This could foreshadow something epic involving the Dragons at the wall. Imagine a battle in the skies, an undead dragon against two live ones. Brothers all. While their mother battles an army of the Undead right below them. Maybe the long battle shoot will involve Dragons too. And maybe one of them will win and head to Wetseros with Daenerys. That would leave Jon to handle the White Walkers on his own, but he is used to the winter cold. We cannot wait for the final season of Game of Thrones.