The Nintendo Switch has been a far bigger success than anyone, including Nintendo themselves, could have guessed. Right now, the system is perennially sold out, even as customers go looking for it in stores- the end result is that Nintendo is literally leaving money on the table by not having enough Switch consoles available.
It looks like the company is responding to the demand by almost doubling its planned production for the Switch this year. According to a report by Financial Times, Nintendo is now looking at manufacturing as many as 18 million Nintendo Switch units by March 2018.
If it actually manages to sell all these 18 million units (an absolute possibility judging by the current sales for the system), then the Switch will have sold 20.72 million units in its first year on the market- sales which put it in the same category as the Wii and PS2. I don’t think that’s a level of success anyone truly expected (though Nintendo have gone on the record stating that they would like for it to happen).