While it's unlikely the Wii U will sustain sales above the Xbox One for any real length this year, It's possible that the Wii U can maintain, or recapture, its lead. But I don't think it will.
If SSB releases early enough during the holidays, it could swing things back for the Wii U. However, given the way other Wii U titles have been delayed, and the ambiguity surrounding the release date, it's not all that certain that it will launch this year at all.
On the other hand, while the PS4 will likely scoop up a larger share than the XBO, multiplatform games should give the system a boost over the Wii U, though the impact will largely depend on what we hear at E3. We've already heard that Assassin's Creed : Unity will be current-gen exclusive; if Call of Duty goes the same route, we could potentially see a significant migration from past-generation consoles.
The joker in the deck is the possibility of a price cut. It could go either way, or both for that matter, but the XBO strikes me as far more likely to make deep enough cuts to make a difference. It has a lot more weight to shed, including a peripheral it could potentially do without, and I'm not convinced the Wii U will drop until the question of whether Mario Kart and SSB can sustain greater sales on their own is answered (Answer: No).
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