Speaking of the Reddit thread, if the theory of that person marrying that person is right, it will really fuck up the story.
I have my skepticisms but I'm not certain I agree with that.
Littlefinger very clearly has his eyes on the North after the Vale. He's the one who set up the Boltons with Jeyne, remember, so he has all the ingredients necessary to simultaneously end their claim to Stark legitimacy and point out that he has a real Stark.
I wouldn't even be surprised if he's involved in Manderley's conspiracy in the books. Or, for that matter, to speculate REALLY heavily, if Manderley was intentionally separating Davos from Stannis in order to more easily perform a triple cross against the Boltons
and Stannis on Littlefinger's behalf.
Regardless, Sansa as Queen in the North is a fairly likely future development so it's mostly constitute acceleration on the show's part, not derailment.
The tougher question is how they'll handle Jon's anxieties over all that. But that's already a challenge the show is going to face.
I still think Brienne and Asha/Yara are still the biggest wild cards this season in the sense that the show's sort of left them adrift. Condensing story lines together isn't something I can get mad about because it's a smart choice for Weiss and Benioff to make, but the leftovers from that abridgment and condensation who no longer have people to interact with can get pretty weird.
I'm still somewhat of the mind that Yara may replace Victarion and with none of the Kingsmoot drama - just have Moqorro show up with the dragon horn or whatever - but as for Brienne, I haven't got the slightest idea. I suppose if Sansa's unveiled in the North (which is still not a development I'm a big fan of - I don't mind her being there, but actually being revealed as a real Stark undermines some stuff) Brienne's gonna make a beeline for Winterfell, maybe?