I have to imagine most Wii U owners either got a Switch or one day will, and there has to be some of the 8.42 million people that bought it on the Wii U like me that won't be double dipping on the game and buying it a second time. That would somewhat limit the sales compared to a new game like Smash where every Wii U owner that bought Smash there will more than likely buy the new game on the Switch. I say Smash should be close but may not reach the sales levels or Mario Kart, but I think the next Pokemon assuming it is done right will one day pass Mario Kart 8.