To me, this potentially raises a serious narrative problem for the show, possibly tied to the shortening and simplification involved in transferring GRRM's very layered world of the books to the film. This may also be compounded by the fact that the show has outrun the books so that the screenwriters are fumbling away a magical logic that, not having been fully developed yet in the books, they do not understand. GRRM presumably has provided a detailed outline and considerable guidance, but based on what we have seen to date, the show is now in a danger zone.
My term for the issue here is "the law of magical integrity." For the story to hold up well over time (think Lord of the Rings), the magic has to be limited in ways that give ordinary mortal characters a dramatically worthy role. Otherwise, mere mortals become spectators as the magical characters hurl mysterious spells at each other, which is not very interesting. The magical elements should also be defined, predictable, and internally consistent, or magic risks becoming an entirely arbitrary deus ex machina, with someone popping up with an entirely unanticipated bit of new magical business to save the day in the final scene or two. In a saga like Game of Thrones, which has now been strung out for five books (and ultimately seven) and eight years of a tv series, jaw-dropping new magical twists shouldn't appear out of thin air in the final couple of episodes. What was the point of all the involved plotting, all the layering, all the prophecies, and all the elaborate character development if, in the end, none of it matters … and the whole thing ultimately is settled by Hermione Granger teleporting in by portkey with the decisive abracadabra triple whacky shazam charm that does the trick? That's a slight bit of hyperbole, but only slight.
If a new magical resolution appears now, it needs to have been well-foreshadowed in the already established lore of the saga. The show has already been sloppy in its handling of Bran's greenseer powers; in the show, his sight is far more omnipresent than in the books, where the greenseers saw through the weirwoods, and perhaps through the actual faces carved on the trees. (This is why the First Men cut down most of the weirwoods.) It would be very disappointing for a character -- who is in fact thousands of years old, temporarily inhabiting the body of young Bran Stark -- to settle an eight year potboiler of a story by using a brand-new set of magical superpowers about which he has told no one. This could have been handled. There are ancient texts in Oldtown that might have provided some foreshadowing. Melisandre might have done so. There might have been ancient prophecies, dimly remembered, that might have given a hint. But none of this has been developed, and it would be cheesy to introduce it now. The show has been too good for too long to go out on a cheesy "surprise, surprise, surprise" note that makes most of the preceding eight years nothing more than an elaborate misdirection.
Well, I guess I saw that one coming, so I didn’t think that was a major plot reveal... If you didn’t know Night King and whatever Bran is, are somehow tied magically, (Ying and Yang) if you will, you probably have zero experience with any sort of fantasy storylines.
Nearly all magic worlds, no matter who brings them about, sooner or later, reveals some sort of balance.... Where the cycles swing back and forth.
I agree though, this was the first time it was explicitly mentioned, so yes this would have been a plot reveal.... So 3 real plot points in the entire episode, rather than the two I stated.
“If a new magical resolution appears now, it needs to have been well-foreshadowed in the already established lore of the saga.”
Maybe the Horn of Winter? I think that Sam still has it from the Fist of the First Men. His ancestral home is even named Hornhill, which might foreshadow his role, in sounding or fixing the horn.
Another one is Sam healing the Night King, maybe with some green dragonglass.