Let's get one thing straight right off the bat:
I've always believed the Xbox One will eventually win the North American region in the next-gen console war. The Xbox 360's dominance still matters and when you factor in Microsoft's relentless marketing, I think it's inevitable.
However, the way it's looking right now, I wouldn't be surprised in the least if the Xbox One finished third behind the PlayStation 4 and Wii U. Now, that may seem ludicrous given pitiful Wii U sales registered in 2013, but Nintendo has been surging as of late, and let's not forget that the Wii U is getting much bigger in Japan. Not coincidentally, that's the same country where you can't even give away an Xbox console.
Europe is PlayStation territory; it has been for years and that shows no signs of changing. If the Wii U continues to stage its comeback in the US (and some newly announced titles might make that happen), and the PS4 at least manages to remain competitive in this region throughout the generation, I think the Xbox One will finish last. It will get crushed in all other regions, especially Europe and Japan, where both the PS4 and Wii U might prove to be much more popular. So, even if Xbox One does end up owning North America, it won't be by much, and it won't be enough to outstrip either Sony or Nintendo on a global scale.
And if the PS4 ends up holding sway in North America, and the Wii U really does end up flourishing in the US and Japan, the Xbox One will get obliterated . It won't even be close. A lot of "what ifs" leap readily to mind, of course, and I'm not saying my prediction is gospel; it's just an observation. But remember, the Xbox One couldn't even outsell the PS4 in June after Microsoft dropped the price to $399. That is not a good sign.