At this point last year, Wii U was at 3.1 million units. By the end of the year, it was at about 5.4 million units. So it grew by roughly 74%.
At the equivalent point in the Xbox 360's life, it was at 3.5 million units. By the end of the year, it was at 8 million units. Growth of roughly 128%.
At the equivalent point in the PS3's life, it was at 3.7 million units. By the end of the year, it was at 9.2 million units. Growth of roughly 149%.
For Wii, the corresponding numbers were 8.3 million, 19.5 million, and 135%.
At this point, Xbox One is at 4.6 million units. For it to reach 11 million, it has to grow by 139% (183% for 13 million). Note that the Wii was massively supply constrained, and PS3 had been out for less than three months in its traditionally-strong region of Europe at the time.
So to be honest, I find it unlikely, given news from E3, that Xbox One will achieve such growth. I'd suggest that a reasonable prediction would be something similar to that observed with the 360 - about 128% growth, putting it around 10.5 million.
On the other hand, there seems to be a fair bit of new momentum for Wii U due to MK8 and Smash. In 2008, from June to December, Wii saw roughly a boost of 56% in total sales, and that was with huge earlier momentum. If we suppose a boost of 70% for Wii U (thereby accounting for the fact that Wii U didn't have momentum beforehand, whereas Wii did), then Wii U would be somewhere around 10.7 million units.
My conclusion? I could see them coming remarkably close to the same numbers. I could also see either one getting ahead of the other, but it all depends on how well the various releases help drive sales. For Wii U, the general lack of momentum is the concern that could see it lag behind the XBO. For XBO, it's the fact that it has high levels of overlap with PS4 in its game lineup, thus potentially seeing PS4 stealing sales that it would otherwise have received.
