I was just thinking, of all the crazy "x is going to become a whitewalker/zombie" that this one seems like it could be a good'un. Assuming Bran survives a bit longer, I can definitely see Zombie-Hodor having a little faceoff with him, Bran being utterly wracked with guilt etc.
I mentioned the "Bran makes the mad king go mad" theory a while back, but the other one I mentioned last week which I can see happening now is with the White Walkers destroying the wall. We now know that the Walkers themselves were created to stop the humans. So whilst we have been under the assumption that the Wall was built to keep the Walkers etc out of the Seven Kingdoms, I think the twist could in fact be that the Walkers constructed the wall originally in order to keep the humans out of the far north (where the Children of the Forest reside).
Can definitely see an epic finale type scene where the Walkers approach the wall and just shatter it with some simple command. Whether it needs to be related to Bran's wristmark or not I am unsure.
It also raises some even bigger questions about the nature of the Walkers, the seasons (summer and winter) in Westeros etc. It was already mentioned way back that the general power of magic in GoT apparently seems to wax and wane with the seasons (i.e. magic becomes stronger during winter, dragons etc). Does this 'awaken' the Walkers and cause them to start building their armies? Or is it the other way round somehow? There must be some sort of reason that with all the time previously, the Walkers have waited until now to make their move, so to speak, and that it coincides with the return of Winter.
Finally, we saw the creation of the Night's King, which is pretty huge. GRRM has often spoken of this 'bittersweet' ending for GoT. It basically turns out that the Walkers were created to keep humans in check and stop them from becoming too powerful. With this in mind, there is an argument for the idea that 'there must always been a Night's King'. Quite possibly this relates to some of Sams maester-research down in Oldtown. Based on the reveals of this episode, it wouldnt surprise me if - after defeating the Walkers - Jon or someone else agrees to become the next NK by being stabbed in much the same way. Then you eventually see the power of fire (Lord of Light - Jon having been resurrected) and ice (becoming the NK). This actually ties in with the whole Azor Ahai stuff, if it turns out that the first Azor Ahai (meant to be the herald of light, fire based etc) was the bloke who got stabbed and became the first NK. Jon being the second Azor Ahai becoming the second NK ultimately, and that it is this internal balance of 'fire' and 'ice' that controls the seasons etc in Westeros.
May as well stop watching now, ive sussed it!