Now that there's no longer a book to base them off of - though it sounds like George R Martin is telling the writers what he had planned - we're not sure what's yet to come in the Season.
An old foe returns. Probably Walder Frey. Someone needs to stick a sword in him, or throw him off a bridge like Balon Greyjoy. His closest ally and Robb's murderer, Roose Bolton, is already dead.
Speaking of Roose, there's no telling what's to come with his son, Ramsay. Sansa, Jon Snow, and the wildlings are going up against him. I hope they have better luck than Stannis did.
And the High Sparrow. It says Jaime faces off against the High Sparrow, but the episode after, the High Sparrow is still active, and so is Jaime, who "confronts a hero" (who could that be? I'd say Tyrion if he wasn't across the Narrow Sea)
As Sansa Said rickon would have had a much better claim than Sansa of Jon, untill they find Bran (Asumming they do) there leadership will be questioned not so much in the north, theuy are loved in the north, but by the other noble houses. Cercsi will be furios at the Starks and the Vale, and little finger if she fins out he was involved. She will have no real power though, as Tommen would listen to The High Sparrow more than her.
I think GRRM said nothing in order to preserve the integrity of the manuscript. The scriptwriters suggested the plot of the whole series to its end in broad strokes, which GRRM confirmed to be similar in its crucial aspect yet refreshingly divergent.
I think the series will split into two big subplots:
South: the Lannisters watching the Freys unravel and fighting the Tyrells who are supported by the unstoppable combo of Dorne, Dothraki and dragon.
North: the Starks arming against the Night's King after his assault on the Wall, which will kill Ed Tollett and end the the remnants of the Night's Watch for the most part.