We've seen a lot of twists and turns but the Lannisters joinning the Starks againsts their allies the Boltons is a bit far fetched
The twists have all been fairly predictable. That one is not.
Agreed on the twists this season being predictable. It makes me think that the book will be drastically different since Grrm doesn't really do predictable.
Personally, I expect the Knights of the vale to show up just as Jon is about to be defeated in order to save the day. I can't remember specific examples but I'm pretty sure allies showing up to save the day when all seems lost has happened a couple times already on the show.
They are predictable in the books as well. Once you realize who and what the story is about everything makes sense and pushes the story to that plot line. Everything has been moved to the ultimate end goal. Now sure there are parts where a number of things could happen and you don't know what will happen, for example Jon has to be in Winterfell to defeat the Walkers but it makes no difference if Stannis defeated the Boltons and gave Jon Winterfell or if Jon takes Winterfell from the Boltons (so who won the Stannis/Ramsey battle was unknown). At the end of the day, this is a story about Jon, Arya, Bran, Dany, and probably Sansa and Tyrion (I've gone both ways with them) and how they shape the Seven Kingdoms and defeat the White Walkers. They all may not make the conclusion of the series, but any of their deaths will serve that ultimate purpose. It is why no one believed Jon was actually dead and why no one believed Arya was going to die in Braavos. It is why no one believes Dany won't eventually leave Mereen and return to Westeros. All of the major twists and shocking scenes were all very predictable. Maybe not in their brutality or how they were carried out, but certainly all were predictable i.e. Ned was too rigid and black and white for the world he lived in, Robb disgraced people who always hated him and would turn on him in an instant, Joffry was just an evil terrible person, etc.
That's easy to say when you watch the show and are on what is essentially book six of seven. It's much more ambiguous in the books.
The examples you've used were indeed predictable, but they weren't the big twists, either. Yeah, if you break everything down to it's most basic level, then everything looks the same. Pizza, Lasagne or a piece of wood, it's all carbs, right? Star Wars or Jesus, it's all "a hero's journey".
If you're really trying to tell me that Ned's beheading, the Red Wedding, the true origin of "the Kingslayer" or Jon's death at the end of book five etc. were predictable when you read that part for the first time, I call bull****.
Yes, for all his twists and turns, Martin does have to adhere to certain basic rules of storytelling, like everyone else. For example, you know that Arya still has a role to play, so you know she won't die in a random encounter. The thing is, you didn't know where the story was headed when you started reading the books, and you didn't know who the real protagonists were. The fact that you don't even know whether Tyrion is a protagonist or not is proof enough that it is indeed not predictable at all.
In a way, ASOIAF was defined by it's twists, so to turn people's expectations on their heads and let things play out in a more traditional way is unexpected in itself.