superchunk on 31 March 2017
WiiU sold about 2.5MM 2MM until it died off. Switch is basically there now.
We'll have to see how Switch does over summer as MK8D and Splatoon land (along with several other games) and its post E3 bonanza before you can claim anything about its launch.
However, ignoring raw numbers, I can say my world of co-workers etc have been much more vocal and have purchased Switches. Only about 10% actually had WiiUs. Granted, it still may be all due to Zelda's awesomeness.
EDIT
Here is my thread where I skillfully tracked WiiU and other systems launches.
http://gamrconnect.vgchartz.com/thread.php?id=151051
WiiU was in stock before XMAS and sold 2.3MM in Nov/Dec 2012. With that in mind, I'd put the die off closer to 2MM.
Switch is already passed that.
