It’s honestly not the issue of running out of book material that concerns me. D&D have two books, a good chunk of The Winds of Winter manuscript and knowledge of the series finale to go on until then. It’s narrative cohesion that I’m worried about. Let me explain:
While the books have so many POV’s, three narratives in particular are its heart and soul: Bran, Arya and Sansa. Their narratives have many parallels, but their perspectives are fundamentally different: One is northern/magical, another is “on the ground” and another is mostly political. They are identity narratives.
Three others, Jon, Dany and Tyrion serve as the hero stories. They are much more external. Their character archs of are essentially about heroes coming into their own. And dragons.
The POV’s of the numerous secondary characters support these six core narratives and revolve around them. Sam becomes a true brother of the Night’s Watch (just like Jon) in the same way that Theon fights regain his identity as a “Greyjoy” just as Arya and Sansa are fighting to remember that they are “Stark”.
D&D have ripped that narrative structure to shreds.
They straight up don’t care about Arya and Bran. Arya’s observance of injustice and her personality as a whole really, Bran’s spirituality and historical awareness, and Tyrion’s less savory character traits: these things probably bored them to death while reading the books. I can just hear D&D’s complaints now:
“Yeah we get, it sucks you can’t walk, but you got a magic wolf who kicks ass so who cares?”
“Just go and start assassin training already.”
"Can we have get back to Tyrion being witty already?
“It was cooler when Jon was just a badass ranger.”
Tyrion and Jon are obviously their favorites, and it’s plain to see why. They’re white, they’re male, they make wise-cracks and they’re the underdog heroes. One of them even kicks ass with a sword. But Tyrion’s story has been watered down to keep him as an uncomplicated “good guy.”
And so where does that leave us? Jaime and Cercei and have huge roles in AFFC, but one has been reduced to a bland good guy and D&D hate the other intensely, no matter how interesting her story is. Will D&D even care about the Greyjoys, or Asha? Where is Brienne going if there’s no Lady Stoneheart? The drama around Myrcella, honestly, always felt like a sideshow. Mayhaps the drama of the Sand Snakes can draw carry the weight.
The narratives in AFFC and ADWD were incredibly frayed and scattered. The strength of the core characters, the Stark children most of all, is what keeps the story powerful and meaningful, and will probably be center stage in TWOW. With a brilliant mind like GRRM straining under the task, I have little faith that D&D have what it takes.
TL;DR, I’m very worried that season five will suck.