It great idea if Nintendo put their first party games on Apple store or Android store but making an handheld/phone hybrid won't work people will still buy Samsung and Apple phones
PS4 - over 100 millions let's say 120m
Xbox One - 70m
Wii U - 25m
Vita - 15m if it will not get Final Fantasy Kingdoms Heart and Monster Hunter 20m otherwise
3DS - 80m