There seems to be 2 versions of NX.
The hybrid tablet / HDMI out version for 2016, and a more traditional console version for 2017.
I feel the hybrid has an instant market. It's more than likely launching alongside or not too far off Pokemon Sun and Moon, and will have special features for those who play Sun and Moon on the new hardware like always. As long as the price is right ($250 or less) they'll launch the hybrid with very strong numbers. I see the hybrid surpassing the sales of the 3DS easily, because handheld is where the majority of Nintendo fans are, it offers a console-like experience via wireless HDMI-out, and hopefully it'll have the majority of features and apps that a 2016 gamer has come to expect of a console.
The NX console; however, is going to have a hard time gaining ground. The PS4 is lead platform this gen, and a mid-life console launch isn't going to change that, and hopefully that's not Nintendo's strategy. The NX console should simply exist to bridge the time between the NX console and it's 2022 successor which would be more inclined to take on the PS5 / XB4 both hardware-wise and technologically.
As long as Nintendo has not only quality, but quantity when it comes to first party games (get a many AAA indie games as possible to re-create old retired franchises like F-Zero, Earthbound, etc...), and gets full 3rd party JP support & at least decent 3rd party west support The NX console will do fine. The NX console will probably be a low seller around 30m - 40m in it's 5 year life cycle (unless it has a hugely successful niche) it's bad in comparison to the PS4 which is already at these numbers, but it's a huge improvement over the Wii U and even GameCube, and puts them back into N64 status, and from there they can grow with it's successor up to 40m - 60m.