I say 40m - 50m, but I really think 30m or 60m, but it ultimately depends on several things.
If they stay the same route they are now with the high price for the device, accessories, games, and misguided online for the entire generation only dropping price down to $249 like the Wii U, then they're doomed to struggle the entire generation and at best will reach 30m, because it'll still do well in Japan, but struggle everywhere else.
NA: 10m
EU: 8m
JP: 15m
RoW: 1m
Global = 34m
If they wise up, pull a 3DS and drop the price to $250 within the first year. Start bundling games with it this holiday. Have holiday sales on accessories and games (which happens regardless, though significantly less on Nintendo). Get Virtual Console up and running and give 1 free game from VC along with 1 free Classic online game for the online subscription. Let digital downloads transfer between 3DS / Wii U. Port/Remaster/Sequel best of Wii U and best of 3DS for the Switch. And simply focus their first party might on the Switch, then Nintendo will have at worst another 3DS on their hands, at best another GBA. The fact is handheld gaming has taken a significant cut in western countries.
NA: 25m
EU: 15m
JP: 25m
RoW: 3m
Global: 68m (Price will determine its success. 30m + 18m + 28m + 3m if they get to $150 before 2020)
The problem is based on history Nintendo is either going to do slightly better than the first scenario. Or do much worse than the best case scenario.







