I don’t think so. It will only be one season I think for the most part.
The Iron Islands stuff has been completely ignored. Even the death of Balon Greyjoy has not been shown yet. Hell, it may never be shown. Point is, the Euron/Damphair/Victarion stuff is out. We’re getting Drone, not the Iron Islands other than through Theon.
Sansa has essentially completed her story arc through AFFC/ADWD in Episode 8 where they were leaving the Eyrie. Harry the Heir may be completely written out. I think we are essentially into NEW MATERIAL with Sansa next season - though “new material” does not necessarily mean TWOW material. It may be things the writers invent to keep her busy while the others main characters catch up.
Jaime is not going north to deal with the Westerlings (who aren’t in the story) or Edmure. The official rumours are that he is headed south to Dorne.
I have no idea what’s up with Brienne and Pod, My guess is that they abandon the search for Arya and will move on to Sansa somehow. I guess we shall see, but it feels like Brienne is going to become a free agent for the writers for the next while.
Bran essentially completed 85% of his story arc in ADwD last night. He’ll have a few scenes at most and then his story moves into TWoW material.
Dany is stuck in Mereen and, like book readers, viewers will be bored silly with that problem. They’ll make up things for her to do and possibly get the Dothraki back into the tale earlier, somehow. I don’t have a lot of hope that D&D can make Mereen interesting. It just isn’t.
Jon has a lot of things to do next season, but it’s all quite manageable. A full slate every episode, but there’s time enough to get him elected Lord Commander, to send Sam and Aemon away, to deal with Stannis and Tormund and the Wildlings and to make a move on Ramsay before we get to his end. A full season – but there’s time.
Cersei does not need much time to have her court go to hell in a handbasket and engage in her competition with Margaery, which has been nicely progressing and set up this season. The pace will be fine.
The fact the Mountain has survived in part and we are shown it means that arc is going somewhere. We may see that next season or at the beginning of the season 6, but it’s no longer than that.
Arya will train next season. A full season, but nothing over the top and not much to leave out really. Easily doable.
Tyrion has some plotting to do with Varys and, maybe, Illyrio. They may have Young Griff and they may cut him out, too. I don’t think that’s necessarily resolved. Then we have Tyrion meeting up with Jorah and getting to Slaver’s Bay. The problem will be how long they can delay that and not bore us all silly.
So that’s the arc for next season and I don’t think that any of it requires more than one season to resolve. GRRM gets with D&D something he does not get with his publisher: an editor who means business, who isn’t asking GRRM to make cuts – they are MAKING THEM whether GRRM likes it or not – and the whole thing will move forward.
Given the popularity of the show, I don’t think HBO is in any rush to bring this thing to a conclusion in Season 7, but 8? Yup, that will probably do it for the show given the increase in actor’s salary costs beyond 7. If there is some material to stretch things out, that may happen, but I think it more likely the stretch will come with TWOW and ADOS, mainly because AFFC and ADwD are such poor novels in comparison to the first three, and in light of the fact that a good solid third of AFFC and ADwD deal with the Iron Islands and characters we are never going to see.
Come next season we are going to have larger portions of it which will come as more or less a complete surprise (Sansa, Bran, Brienne and much of Jaime) . And unless TWOW is released in 2015 (and, to be clear, I think it will be) we will ALL be unsullied for Season 6.