Nintendo is in a beyond prime position. In the grand scheme of things no one really played the Wii U. The Wii U has at least a dozen system sellers that rank as some of the best critical reviewed games of the generation but still plenty of question marks. Nintendo could simply release super Mario 3D land, Mario Marker, Bayonetta 1/2, Xenoblade Chronicles X, Super Smash Brothers, Super Mario Bro Wii U (with all the DLC) and each of those would sell at the very least 2-3 million units without much effort.
While they rerelease those titles they can sit back, polish games that were developed direct for the switch and ride the second and third wave of it's life on easy Street while still release games that everyone considers system sellers.
It can continue demand like this for the next 12 months without hassle, all while releasing Wii U games. 18 million units sold by March 2018? If they show Pokemon this E3 for the Switch you can damn near add a zero to the end of their estimate and that would still be within the realm of possibility.
