OK, I’m going to try to voice what I think is the problem in the fandom with the Arya stuff, but I don’t know if I can express it very well. Here goes nothing...
The story GRRM is telling is a large and complicated one with multiple layers of foreshadowing and different prophecies which misdirect and, on other occasions, overlap. However, he is still telling a story about characters and their development. He has said on multiple occasions that he is telling the only story that matters - the one of the human heart in conflict with itself. To that end, the show has done a grand job with certain characters. Theon’s character arc was perfect. He died as Theon, protecting his home. Spot on.
Now let’s imagine Harry Potter and assume on the Half Blood Prince has been written. Imagine that the movie of DH part 2 comes out and, at the very last moment, it is Neville Longbottom who kills Voldemort. It was legitimately prophesied and foreshadowed and it was a perfectly acceptable story arc for Neville. But what does that then mean for Harry? What was the point of his story arc? What about Hermione, and Snape and Ron and all the other characters who were part of Harry’s story? I suppose Harry could then go on to be chief auror or something like that, but his story would seem somehow.... unsatisfying.
D&D mentioned that they decided about 3 years ago that Arya would be the one to kill the NK. It seems that they made this decision as everyone was expecting it to be Jon. Fair enough, their MO seems to be to totally surprise the audience with the utterly unexpected. I’m not bothered about the effect of this on Arya’s story arc, but the effect that this will have on Jon’s and his supporting characters will be more difficult to resolve.
It seems clear that there will be a point where Bran/Sam/Sansa will use the information about Jon’s parentage to oust Dany, but why would this be narratively satisfying at this point? If Neville was the one to kill Voldemort, why is Harry the hero any more?
I will wait and see...