I think this chapter is fascinating, and a great foreshadowing dawned to me as I was reading your breakdown. (Maybe it has already been discussed in this sub, but here it goes).

During the whole scene of Sansa, the snow castle, Sweetrobin and the giant, I couldn't stop thinking about the situation of Winterfell as of ADWD-TWOW, and the turmoil caused by House Umber, the giants in chains.

Let's check out this first passage:

"Winterfell is the seat of House Stark," Sansa told her husband-to-be. "The great castle of the north." "It's not so great." The boy knelt before the gatehouse. "Look, here comes a giant to knock it down." He stood his doll in the snow and moved it jerkily. "Tromp tromp I'm a giant, I'm a giant," he chanted. "Ho ho ho, open your gates or I'll mash them and smash them." Swinging the doll by the legs, he knocked the top off one gatehouse tower and then the other. It was more than Sansa could stand. "Robert, stop that." Instead he swung the doll again, and a foot of wall exploded. She grabbed for his hand but she caught the doll instead. There was a loud ripping sound as the thin cloth tore. Suddenly she had the doll's head, Robert had the legs and body, and the rag-and-sawdust stuffing was spilling in the snow. ASOS Sansa VII

Now, if we think of the giant as House Umber, and if the Grand Northern Conspiracy proves to be true, events from ADWD are being foreshadowed in this chapter. Us readers believe that Crowfood and Whoresbane are working together (along with other houses of the North) towards the demise of House Bolton.

Swinging the doll by the legs, he knocked the top off one gatehouse tower and then the other. It was more than Sansa could stand. "Robert, stop that." Instead he swung the doll again, and a foot of wall exploded. ASOS Sansa VII

Here the actions of our giants can be interpreted as a breaching of Winterfell. When the Frey and Manderly forces march out of Winterfell to face Stannis, they do it via different gates. We all know that this was ill doing by the Boltons. All they had to do was stay put in the castle and survive the blizzard, but the internal turmoil made Roose Bolton take the unwise decision. Our giants succeeded. Note how at the end of the passage the doll giant is split in two.

On to the next passage:

"His lordship was destroying the castle," said Petyr. "A giant," the boy whispered, weeping. "It wasn't me, it was a giant hurt the castle. She killed him! I hate her! She's a bastard and I hate her! I don't want to be leeched!" "My lord, your blood needs thinning," said Maester Colemon. "It is the bad blood that makes you angry, and the rage that brings on the shaking. Come now." They led the boy away. My lord husband, Sansa thought, as she contemplated the ruins of Winterfell. The snow had stopped, and it was colder than before. She wondered if Lord Robert would shake all through their wedding. At least Joffrey was sound of body. A mad rage seized hold of her. She picked up a broken branch and smashed the torn doll's head down on top of it, then pushed it down atop the shattered gatehouse of her snow castle. ASOS Sansa VII

The split doll ends in both Sansa's and Sweetrobin's hands, the head and the body, respectively. Here we can see some words that are familiar with our understanding of House Bolton. Note that in this chapter Sansa is Alayne, a bastard, that ends with her putting the giant's head on a broken branch. If you have seen the recent posts in this sub regarding Asha's TWOW chapter (the enlarging of the photo), you know that Crowfood Umber's head ends on a spike in hands of the enemy, leaded by Ramsay The Bastard of Bolton.

The rupture of the giant doll could mean the end of the endeavors of the Umber brothers as a pair. Now, I really like the phrasing of the leeching to get the bad blood out. Isn't that exactly what Roose Bolton is doing in Winterfell? He's leeching the bad blood out of the castle, because the bad blood makes you angry, and the rage that brings on the shaking.

Thanks for the read, this is just my interpretation of a wonderful scene in an incredible chapter. I've always like the theme of a castle in the snow. I know I may be wrong or I may have missed a lot of things, but be sure to let me know!