I don't expect to see anything that special, although I am expecting that they bring out a special edition Nintendo Wii that has a Zelda theme, or is at least green, like they did for the 25th anniversary of the Mario series. They will probably go through the entire re-advertisement phase that the Mario series had as well, in which a lot of it's more recent games were advertised pretty much 24/7 (although I think the price of each game was reduced).
Although, I guess that the surprise could be something to do with Skyward Sword. I wouldn't have thought that the game would be the surprise though, because not that many people would be surprised. In fact, I'd be pretty disappointed if that was the best surprise that Nintendo could gather. I think it would be something more along the lines of a collectors item (like the little figurines that they were giving out when they first released Pokemon Platinum).