Ideally, the sixth and seventh books should see GRRM trying to unite and conclude several different plotlines and set up the final conflict, but he's either incapable or unwilling to do that. I think the show's ending is partially based on his ending, as it does have all the elements and themes of his subversive narrative, albeit rushed to meet an artificial deadline. (In war, there are no good guys, one side's hero is another side's villain, the death caused by war outweighs all the potential good it may cause, etc..) So yeah, part of his hesitance may be due to the show being so poorly-received when it adapted his ending. If D&D had their way, Jon Snow and Dany would just win with their trademark generic good-guy talk, and they'd have just ended up mating on the Iron Throne after the deaths of Cersei and the Night King.
I sincerely believe King Bran is something Martin conceived of, and is not a D&D invention precisely because D&D hated the magic of the series and minimized it as much as possible. That said, getting a boy wizard to rule Westeros requires all other competitors be dead or out of the running and the country itself reduced to some sort of post apocalyptic state.
Thing is, Bran may be the central character(he is the first POV after the prologue) but he isn't remotely the most popular or interesting.
That's a big problem. He kept piling on plotline after plotline. There's also the Euron plotline to add to all that mess. The problem with GRRM was that there was no one to reign him in and force him to focus. It's the same problem George Lucas had when during the time when he was writing the Prequels, there was no one to tell him "no". The difference is that Lucas had an outline that he stuck to, which at least allowed him to end the Prequels on a hopeful note, whereas GRRM is just going around his world, following random plotlines, adding to the bloat of the story when he should be chopping things down and getting things to a close.
Like say, whey not have Stannis and Lady Stoneheart join forces with Petyr Baelish and the forces of the Vale? You'd unite three separate plotlines into one, and the three of them have different reasons for wanting to see the Lannisters fall: Stannis has honor, Stoneheart has vengeance, the forces of the Vale hate the Lannisters for supposedly killing Jon Arryn, and Littlefinger's a greedy little shit. That's what I'd do in his position to cut down on the fat and set up a coherent ending.
My general prediction(for Winds).
Stannis wins at Winterfell but Rickon is found and the North more or less deserts him at his moment of triumph. Jon is also resurrected meaning Mel loses faith in him.
Aegon smashes Mace Tyrell before the walls of Storm's End and King's Landing falls, Tommen and Myrcella die in rapid succession but Cersei flees.
Euron blows up Oldtown but Victarion escapes his control. He may or may not get a dragon.
Dany gets the Dothraki(the scene in the show is pretty similar to a vision Dany has in the books) and goes west, Tyrion and the rest of the Mereen cast head west along a separate route, they meet at the Narrow Sea-Illyrio probably dies at the end.
LSH infiltrates Riverrun(with Jaimie forced to help her) and massacres the Lannisters and Freys thus throwing the Riverlands into a revolt and giving the Vale an opening to intervene.
Stannis dies at the end-Shireen is sacrificed just as the Wall falls.
Dany makes for Westeros, Sansa heads North as does Arya, Bran escapes the cave, "hold the door happens", Tyrion and Dany meet, Cersei goes to Casterly Rock and Jaimie probably heads north. Not sure about LSH or Sam or where some of the other characters will be at the end of Winds.
^at least that's my general guess as to what Winds will be like. Not that it matters as its not coming out.
That pressure used to exist, especially after the last season of the show crashed and burned, but now, there's just apathy. No one cares anymore, outside of the diehards who still think that Martin is some kind of 4D-chess player when really, he's the lesser, hippie-modernist version of Luo Guanzhong or William Shakespeare, nowhere near the literary genius of Tolkien, or those other two authors.
Yeah his legacy is doomed. And that has to have sapped his motivation even more.
