The Wii U died the moment it was conceived.... Which was 2008? In all seriousness though... 2017 or 2018. Nintendo kind of drops support quickly when a new platform rolls out, which I expect will be sometime in 2017/2018.
PS4 will live till at least until 2025...
Xbox One 2020.
Current gaming platforms - Switch, PlayStation 4, Xbox One, Wii U, New 3DS, PC