Look at the strategies behind all of the consoles, find the pattern, then consider what Nintendo will do with NX.
They were all traditional consoles, and declined in sales from the predecessor. Wii took the world by storm with waggle, but once people stopped caring about that after only 4 years, its sales fell off a cliff. WiiU had Nintendo going back to being a traditional console and, well....you see the trend continue.
NX will have to do some obscure thing that'll make people say "I wanna play this way instead of with just a regular controller" because traditional gaming is, and has been, on the decline for Nintendo home consoles.