Both wii and wii u sold a lot of consoles at launch about 3 million in similar time, one had demand that outstripped supply for many months and the other sales dropped off a cliff shortly after launch.
The issue is how much real demand is there. If you say there is 5 million of Nintendo core audience, 20 million of potential customers who may get on board depending on price and game quality and maybe 80 million of very casual buyers who really need to be convinced that its a must have item by media reports and friends then you have to work out how far the Switch appeal will go.
Even if it fails shortly after launch its not like Nintendo can't price drop though anyway. They have set accessory and game prices very high so even if they had to subsidise the retail hardware price of consoles a bit they would still be quids in. The Switch hardware is probably hugely profitable currently and would probably remain profitable even with a heavy price drop although of course Nintendo needs to still claw back a huge amount of R&D invested in the Switch design. Lowering the price would slow the rate of re-couping that money.
