No one said that the NX will mark the next generation. While the WiiU was a little early for this generation, the NX will be a little late. Nintendo just doesn't fit in the cycle with Sony and Microsoft anymore, because Nintendo consoles aren't really an alternative to PS and XBox anyway. People buy them either because they are die-hard Nintendo fans or as a secondary platform. I reckon it will be the same for NX, except if Nintendo presents something really revolutionary.
No respectable company releases two consoles on the same generation. The NX isn't a little late, it's VERY late. And Nintendo does compete with Playstation and XBox, whether they like it or not.