I find it hard to believe Martin would feel rushed to properly close all the major story beats within the confines of at least 2000 pages. (assuming at least 1000 for the next to books)
That sounds like a lot of pages. But then you consider the actual story:
You have Sam in Oldtown with Jaqen and Sarella Sanda. You have to have the whole story with what Jaqen/the Faceless Men are doing there, why Sarella is in Oldtown, the whole storyline with Marwyn's group and their conspiracy, the actual main faction of the maesters (and the last chapter in Feast plus Lady Dustin's comments in Dance make it sound like there will be some plots and conspiracies with the Archmaesters to learn about), and learning more about the idea that most historical records in Westeros are fake, not to mention Sam actually studying and becoming a Maester. Plus, at some point you're probably going to have Sam learning about Jon's death and the situation on the Wall, more stuff with Gilly, dealing with his family situation, and eventually probably returning to the Wall/playing a role in the final battle.
Arya has all of her training with the Faceless Men to undergo, and judging by where her story ended in Dance, that will probably be pretty significant. During this time, there's also going to be more information about what the Faceless Men's goals are, and what role they've played in historical events. Then Arya is going to have to eventually have something happen with Needle and Nymeria, her skinchanging abilities, and reunite with the rest of the storyline in some way. (She doesn't necessarily have to reunite with Sansa/Bran/Rickon/Jon, but she has to eventually connect with some plot point)
The Meeren storyline has a lot going on, but at the very least, we have the upcoming battle with all of the various forces from Volantis etc, the situation with the Pale Mare, Barristan trying to deal with stuff in the city, finding out the truth behind the Harpy situation and who was responsible for the poisoning attempt, etc. You also have Tyrion and Jorah with the Second Sons and how they're going to get them to change sides. Eventually, they'll have to cross paths with Dany (and probably Aegon for Tyrion, at least), and Tyrion has to return to Westeros, deal with Casterly Rock, meet back up with Bronn in some way. There's probably a lot more going on with the Second Sons, too, given how much time they've gotten. Then you have Victarion's incoming arrival, Moqorro's presence with him and what his goals are, the purpose the Dusky Woman, the use of the dragonbinding horn, and an eventual showdown between Victarion and Euron. Plus, there's been too much teasing not to have some meeting between Victarion and Dany at some point. Dany herself has to deal with the Dothraki in some way, likely by fulfilling the Stallion that Mounts the World prophecy about uniting all the Dothraki (it was probably always about her and was simply erroneously read by the crones as being her son), and then return to Mereen in whatever shape it is in. Given that Martin said that Maggo would play a significant role in the book, and we've heard enough mentions of Khal Pono to think he'll show up again, I think uniting all the Dothraki won't just be a two chapter thing.
Oh, and even after all of that stuff in Mereen is resolved, Barristan has already promised the Windblown to help them capture Pentos (and we're probably going to find out more about the Tattered Prince's past via this), and there's a lot of discussion in Volantis about an impending slave revolt that has the nobility worried and slaves waiting for Dany to come and free them.
In the south, you have Dorne's eventual learning about Quentyn's death, plus how they'll react to Aegon and deal with him. Arianne's storyline has a lot of ways it could go, but she's probably going to marry eventually and also have to take over from her father, because I can't see Doran surviving the series with his health. There's still the mystery about why Darkstar tried to kill Myrcella, and why Doran considers him the most dangerous man in Dorne. There has to be more than meets the eyes here. There's a lot going on with Connington and Aegon as well. You have questions of Aegon's past that will eventually come up, as well as him learning how to rule and maturing. Plus, there's that impending outbreak of greyscale Jon is sure to cause, and we hear a lot about greyscale in both the Tyrion/Connington chapters as well as from Val.
Brienne/Jaime/Stoneheart have to have their current situation resolved, and then proceed on in some manner. I'm not really sure where any of these characters are ultimately headed, and there's probably the least difficulty in terms of resolving their stories in a timely fashion here. The Brotherhood probably still have a significant role to play, especially with Tom stationed in Riverrun. I would guess that Gendry has some further role to play, and we'll probably hear about Ned Dayne and his splinter group at some point in the future. The eventual changing of hands of Riverrun, the whereabouts of the Blackfish, and what happens to Edmure in his captivity (and inevitable release) all sort of fit in here.
Then you have Sansa's storyline in the Vale with Littlefinger, and the possibility of her being crowned as Queen. We're going to meet Harry the Heir eventually, and Bronze Yohn's opposition to Littlefinger will come to a head. We also know from the end of Feast that Ser Shadrich, who was looking for Sansa, has found his way into Littlefinger's service. This would also be a logical place for the Blackfish to pop up, and there's the question of what Robert Arryn's fate will be, and how Sansa will come into her own as a player in the game of thrones (which seems the logic place her story is heading).
In the Iron Islands, you have the Damphair running around trying to raise up a rebellion against Euron. This is probably going to go somewhere, and the past between the two characters is going to be revealed in some way. The Iron Islands story is probably the least difficult one to resolve in two books, but some significant changes will almost certainly be coming to the islands. The Shield Islands situation will also probably be addressed at some point in Winds.
At Winterfell, we have the questions about the Pink Letter's legitimacy, and the upcoming battle between Stannis and the Boltons, as well as Manderly's plans. Eventually, we're going to see the deaths of the Boltons and Freys, and find out more information about Lady Dustin and her past. Stannis still has a lot of stuff left to do, and now he has Theon and Asha with them. Dance sets up the possibility that Theon could be used to contest the Kingsmoot, and his redemption storyline, hearing from Bran in the weirwood, and connection with Jeyne Poole will be developed some, as well as Asha's plans to reform the Iron Islands. Then you have Davos heading off to Skagos to find Rickon and Osha. That alone will probably take some time, and then you have Davos bringing him back, meeting back up with Stannis, continuing as the hand, probably having some further interactions with Melisandre, and having some sort of contact with his wife and younger sons again.
The situation at the wall with the wildlings, Jon's death (and possibly coming back), Melisandre's motivations, etc is also really complex. This could fall out in a number of different ways, before even getting to Others eventually attacking, and us finding out what their deal is. Beyond the wall, we also have Bran and Bloodraven, the fate of the Reeds, seeing where Bran's story goes and what further information he can find out through his new powers, and learning what Bloodraven's motivations are and what the Children of the Forest are up to. Plus, Coldhands identity and role in all of this.
And then you have the shitstorm about to drop in King's Landing, with the deaths of Kevan and Pycelle and the upcoming trials. Robert Strong's identity has to get revealed in some way, Tommen is almost certainly going to die, we're probably going to get close to an all out war between Cersei and Mace, which will also have Nymeria Sand showing up in the midst of it, and the High Septon scheming for some purpose that we'll have to find out about eventually. Plus, Varys is still running around up to something in the city, Qyburn's whole deal remains a mystery, Loras's fate is very much up in the air, as is Aurane Waters, and not too far from King's Landing we have Bronn gathering up an army of sellswords.
And that's not even touching on everything. There's tons of other things that will come up, which I might have forgotten or just not put on the same scale as these things. And this is even if Martin doesn't introduce a single new plot point in the final books. I simply don't see any way that all of this could be put in ~2000 pages without it being a complete rush job with things being barely more than outline at times.
