Nintendo has spoken about the NX. Officially and on the record, not via industry rumour. In a financial presentation it says the Nintendo NX machine will appear in March of 2017, all around the world. In shops. To put where the Gamecube used to be. Fact.
The news has been embedded on Nintendo's official web site in an official financial statement for additional official status, meaning it's literally, definitely official. The PDF can be found here, and it states that: "For our dedicated video game platform business, Nintendo is currently developing a gaming platform codenamed 'NX' with a brand-new concept. NX will be launched in March 2017 globally."
That ought to be official enough for anyone.
With regards to its current hardware, Nintendo was even brave enough to use the word "blockbuster" to describe a couple of Wii U games, saying of their performances: "With respect to Wii U, Splatoon sold 4.27 million units and Super Mario Maker sold 3.52 million units, both becoming blockbusters and contributing to energizing the Wii U platform. In addition, The Legend of Zelda: Twilight Princess HD, which was released globally in March, got off to a good start. The global sales of the Wii U hardware and software reached 3.26 million and 27.36 million units respectively." [Nintendo]