I've never seen this guess anywhere else – so it is, as far as I know, unique – but it should also be considered a major spoiler, even if I'm later proven wrong. This is extremely speculative, and fiction doesn't follow the rules of real life, so there's not really any predicting it with certainty even if your theory is rock solid. As I've mentioned before, ASOIAF is great literature and you should enjoy it without any preconceptions.

That all being said, continue if you wish.

I'll try to add more vertical space to avoid accidental spoilers.

Here's my guess: Jon Snow and Daenerys Targaryen sacrifice their child to the Others to stop the war. The child is the Prince/Princess that was promised, and (because prophecy doesn't promise things) was promised to the Lands of Always Winter to keep the peace. The Others are deeply magical, and want someone of magical heritage, so this seems like a solid guess. An early leader of the Night's Watch sacrificed children to the Others, and it's possible that only Craster doing so in the recently history of the story has been pushing their treaty to the breaking point.

A lot of the other clues are slightly metaphorical, although you have to admit, it would feel like plunging a flaming sword into your chest, having your son taken from you and given to monsters by the one you love. It's possible this message will be delivered by the spirits in the crypts of Winterfell, but that's the type of mega-speculative guesswork that dooms people. The basics, of their sacrifice to the others, is the core here. I don't think Jon will kill Daenerys – that's by far the most popular theory I've seen but "I need to craft a powerful sword" is a deeply strange thing to plug in the end here. Maybe she dies in childbirth – I suspect not, but this theory works either way. Jon himself may be turned into an Other – if they are able to do the same conversion they can do to babies – but if they could, why not capture more humans and convert more of them? I suspect that won't happen.

Anyhow, be prepared for an update later about the veracity of this prediction, and whether I will hold out more hope for the books.

Bonus predictions: The Hound is the Valonqar [edit, after seeing 8x01: Euron?]. The Night King's name is Jon Snow. The Iron Throne is either retired from use or destroyed.

[edit after 8x02: obvious inference is that the Night King has been taking his time because he's been uprooting the weirwood network, and is moving swiftly between northern holdfasts and such because that's where all the remaining weirwoods are south of the wall – also explains why the intro seems to highlight the Isle of Faces, and why Bran would want to wait in the godswood, despite his powers seemingly not needing the weirwoods in the show – continuity with the books and the pivotal moment that needs to take place there].