The Switch was exactly what Nintendo needed after the Wii U disaster, but I doubt anyone at Nintendo predicted just how popular its hybrid console was at launch and would continue to be 10 months on. It's so popular that Nintendo president Tatsumi Kimishima just set a very high new target for sales during fiscal 2018.
As Gamesindustry.biz reports, by April 2019 Kimishima wants Nintendo to sell another 20 million Switch . By April this year, Nintendo expects to have sold around 17 million units, so by April 2019 they expect the total to increase to 37 million. That pegs sales at a rate of 1.6 million a month, meaning by December 2019 the Switch could reach the 50 million mark.
Of course, this sales prediction relies on the hardware selling as well as it is now for years to come. That will only be the case if Nintendo continues to produce games we all think it's worth buying a Switch to play them on. For most companies that would be a difficult ask, but this is Nintendo, which is a company overflowing with IP that sells millions of copies every time a new game launches.
If Nintendo can continue to produce games carrying the Mario, Luigi, Zelda, Kirby, Pikmin, and Pokemon names at regular intervals over the next two years, nobody would bet against the Switch hitting 50 million units or more. It also looks as though the competition will help. Nobody expects any new hardware from Sony or Microsoft in the next couple of years, so there will be no distractions for gamers beyond new games.
If Nintendo does reach 50 million units by December 2019, it will have beaten the PS4 which took almost exactly three years to reach that total. The Switch would do it in 33 months, beating Sony by three months.