2017 for sure, here's what I think/hope they do.
Early/Spring 2017 they will do a conference to announce the Wii U successor and release it the same year, lets be real here, they will likely see from what Sony and MS did that they don't need to announce a console a year and a half before it releases, and they won't announce it in a simple Nintendo Direct because a new console is MUCH bigger then announcing a new game, I'm hoping they do what Sony and MS do and really hype it up.
Also I'm hoping it releasing alongside the PS5 or Xbox Two because then it will hopefully be able to be on par or at least almost on par with them spec wise.
It won't be released in 2016 because that's just 4 years of Wii U and 2016 will be the year for the 3DS successor.
And also, any game they make that will be releasing for the Wii U in 2017 will also likey have a Wii U successor version as well, that way they can make the launch better, if the next 3D Mario takes a while to release I could see them pulling a Twilight Princess on it.
