This holiday will have Smash Bros for Wii U, which will move units, and Halo: MCC, which will also. We'll see how reasonable claims like that are after the holidays.
The same thing is true about next year for Halo 5 for Xbox One. Star Fox and Zelda will help the Wii U seem to have more major games that people care about.
The real question is how many people that seek these core games that have long been guaranteed already have the system. Nobody bought an Xbox One not knowing that Halo would come to it, and the same thing is true for major Nintendo games on the Wii U.
I think Xbox One has some advantages in that it has online games that will draw people's friends in and keep people playing for long periods of time. Even with Smash, many people that want to play will just go to play against their friend at their house and not buy a copy or system of their own, since playing together is key to the game's target audience. Xbox One also has some lingering Xbox 360 loyalty and more media features and apps.
It's not impossible for the Wii U to sell better though, especially if Smash does amazingly this holiday season. I somewhat expect them to stay relatively close at least until 2015 holidays.
