If it's already close to completion, one would think it would be another Wii U title.
I kinda think after 2015, they won't release anything major on the Wii U in 2016. But who knows, I could be wrong.
Nintendo has said they're still committed to the Wii U through 2016, so there's no reason to think this would be any different. I could see it being a cross-platform title, on the 3DS, Wii U, and possibly the new 'NX' platform, but with the Zelda Wii U game still forthcoming in 2016, I don't see the Wii U being a dead platform until at least Q1 or Q2 2017.