If comparing tracking is your argument, why would it pass 100 million, if it's tracking below the Wii? Significantly below, too, since Wii did almost 26m in 2009 FY. Unless you mean the Wii was sabotaged somehow, which is eh...
Besides, the 3DS was an unique slow burner as far as modern Nintendo hardware goes. It sold more than a third of its lifetime sales after four fiscal years in the market. Don't count with the egg before it hatches etc.
The Wii was cut short early when Nintendo effectively abandoned it after 2010 when development was moved to 3DS and Wii U. There's no reason for them to do the same with Switch as they no longer have to worry about supporting two different product lines. As such, the Switch will likely have significantly better legs than the Wii beyond Year 4.