It has already been mentioned, but the Japan factor alone means it won't be as large an impact as the 3DS. Besides the fact that handhelds sell significantly more there, the Wii U lineup can't compete with the 3D land/Mario Kart/Monster Hunter/massive price cut that the 3DS had in 2011.
Even if the Wii U were to start following the Wii sales trajectory starting in October, it would still be far behind. After nine quarters the 3DS has shipped 11.54 million in Japan. If the Wii U does manage Wii sales, we'd be looking at ~5.35 million in the same time period. Of course, that is only if the Wii U can somehow match Wii sales. Considering it sold more in six weeks of the 2007 holiday than the Wii U has in seven months, that will probably be a tall order.
