At this point it would not be too surprising if the SNES Classic eventually went one to surpass the Wii-U in terms of worldwide sales.  As of right now it looks like the Nintendo Switch is definitely going to surpass the Wii-U in terms of overall sales.  As it currently stands the Nintendo Switch has sold more than 7.63 million units worldwide in less than a year while the Wii-U has reached over 13 million units in total.

While the SNES Classic is popular right now it’s kinda hard to predict whether or not it will surpass the Wii-U in terms of sales within a few years.  But then again we probably won’t see another retro based game console like the SNES Classic for a while.