The Nintendo NX will officially launch in March 2017 alongside a new Zelda game. This was confirmed earlier via a tweet from Nintendo saying:
— Nintendo of America (@NintendoAmerica) April 27, 2016
Right now very little is known about the Nintendo NX, but it is expected to use an AMD SoC that is more powerful than the SoC used in the PS4. It has also been announced that the next Zelda game has been pushed back to 2017 and will now release on both the Nintendo NX and Wii U simultaneously.
The Wii U has been a massive failure for Nintendo even though several games have been well regarded by users and critics alike. It is so bad that it now longer has any 3rd party support and the 3DS showing its age on the handheld market. So it will be critical for them that the new Nintentendo NX is a success.