It's iffy to call something that popular a fad, but considering how noone gives a fuck about motion, and noone cared about the WiiU at all, is fad really the wrong word for the wii?
What do you mean, no one gives a fuck about motion? Motion has been around for ages and is here to stay.
PC mouse is a form of motion control and is lauded by many people as being superior to joysticks. The Wii's best motion control was as a pointer, which wasn't far off from mouse control, and plenty of people have said for FPSs, mouse > motion pointer > joysticks.
Everyone has motion control built into their standard controllers except MS. Motion assisted aiming is awesome and intuitive and deserves to be an option in many games these days.
Plus without the Wii laying the groundwork and igniting public interest in motion control, we wouldn't have seen the sudden spike in research, funding, development of motion control systems, which have ultimately resulted in the first consumer grade VR. Motion control is 100% necessary in VR because you can't see where your hands are, accurate detection of the controllers means you can feel like you are actually inside and interacting with VR. It's also given us the necessary head tracking systems and other advancements in detection of the human body and its positioning.
Motion was big, and is still big.