Not all 3DS owners are Nintendo fans... but sure they having 40M fans (if that was the case) doesn't mean it will sell 40M. N64, GC and WiiU sold less than 40M, all Handhelds sold more than it. And numbers so far indicate a better chance of Switch doing 70M than 40M.
Agreed. But Pillertriller suggested Nintendo only sells to Nintendo fans.
Actually I think, if you purchase and like a console of Nintendo, you're probably a Nintendo fan. Even if it is your first one, so you're a freshly converted Nintendo fan. Therefore the number of fans is volatile.