Still early to make reliable predictions. I don't think Nintendo have satisfied their core audience yet in numbers, that might be 6 million and then we have to see how it attracts a wider more casual audience. It still feels to me that like the DS and DS lite situation the real Switch seller will not be the mk1 console but a smaller cheaper mk2 version.
However the reality is its based on a scalable architecture that will improve with time. The wii u was end of line and the last powerpc based console we will ever see. Nintendo have adopted pretty standard technology with Switch so what would have been a standalone model can now be updated with newer more powerful systems with fallback compatibility modes. By this nature alone the Switch will sell far more than wii u because it represents a range of gradually improving models rather than a single model.
Really the debate is how many mk1 Switches will be sold before the new improved mk2 model will be launched. I can see the Switch brand being used many years into the future so difficult to predict numbers for the complete Switch range. What if Switch models are still being produced into 2030 but those models are 10-30x more powerful than the current models do they still count in the numbers which could for the complete range lets say be 100-200 million or perhaps even more.
As ever it will be interesting to see how it unfolds with Nintendo.
I do feel the current success of the Switch is fragmented which isn't uncommon in gaming, some markets have taken to it strongly others more resistant to it. Sometimes you see one person stating its not selling too well in their country and another saying it's selling very well in their country and there is denial about the other's opinion which is a bit ridiculous because clearly both can be true.
