They'll probably just talk about how it did in sales and how it brought in new gamers. Maybe they'll show a montage of great Wii games. They'll try to talk about why Wii owners should make the transition to the Wii U.
I also think that a guy will come out dressed like a Wii. He'll pass a torch to the guy dressed like a Wii U. Then, he'll die on stage. The Wii U guy will say, "Don't worry, old friend. I won't let you down." Then, the audience will cheer.