Here is an interesting thread that shows peoples thoughts about the Switch's success before it launched. Really, there were lots of 10 million lifetime predictions and these were not Nintendo haters who were making these predictions. Even Nintendo was really low on its own forecast (which was probably deliberately optimistic when it was made).
https://gamrconnect.vgchartz.com/thread/225013/dfc-intelligence-believes-nintendo-switch-can-shift-40-million-units-by-2020/1/







