The first impression from internet looks really good. It's nowhere close to what was the Wii U back in 2011, where people didn't even knew was a new console... the youtube trailer is now at over 15 million views in only 3 days, already half of PS4 in almost 4 years.
Basically Switch is what the Wii U should have been. Switch will combine the fanbase of handhelds and home, and about Nintendo handhelds, those always sold incredible well. Even if "3DS is a flop" for some people, that thing is going to sells over 70 million lifetime. And won't sell more than that only for the simple reason NX is coming, cause as for now, sales of 3DS are incredible great for a 6 years old system. Pokémon GO showed how there are still many people which are going to buy an handhelds, 3DS is right now selling way more than what was selling in the lasts 2 years, it's basically get a second short life after Pokémon Go, and before Switch will release, it will have an amazing holidays with Pokémon moon and Sun and the release of Mario Run, which will boost by a big margin the Super Mario interest on people, like Pokémon GO did with Pokémon.
When Switch will launch in March 2017, the two biggest Nintendo IP ever (Pokémon and Mario) will be stronger than ever, and there is Zelda Breath of the wild too at launch, which has a chance to become the biggest Zelda game ever, or at least chart in the TOP 3 after Ocarina and Twilight Princess.
With a right price ($250 my guess), i have almost no doubt it will have a big launch. After that we'll see, much will depend on the third party support, the general line up, the lifetime of the console ecc...
2020 predictions: NSW 21m, PS5 6m, XSX 4.5m, PS4 9m, XB1 3m
(PS5 and XSX predictions will most likely change after we know enough about them)