Spoilers (discussion of books!)
I know it's kind of silly to speculate based on one and a half minutes but I'm honestly surprised by how many people are convinced that this is Coldhands on twitter and WIC.net. Aside from the fact that you can't really see if it's eyes are blue or not, I seriously can't see why people are so sure. Haven't we seen White Walkers in clothing and on horses before? And Coldhands wears clothing that makes him immediately noticeable as one of the Night's Watch and his head is covered. And he rides an elk. I can see them taking some liberties with the elk maybe but completely ditching the Night's Watch element? I would love confirmation that he is going to be in the show but this seems like a stretch.
But damn, is that a fucking awesome and scary shot. That trailer was great.