The impact the Switch had on the market, in terms of both sales and marketing, has been much stronger than the Wii U's so far, and it's comparable to the Wii's. This alone is a guarantee that Nintendo will support it in the future, so expect a remarkable batch of first-party games by the end of its lifetime. This is extremely important to Nintendo consoles, because first-party games alone can justify its purchase (if they're to your liking, of course).
The concept itself is wonderful, and this is what the Wii U should have been in the first place. However, aside from the hybrid configuration the console has, its hardware specs are nothing to write home about, which was needed to keep the price reasonable: on the other hand, though, this means that, sooner or later, third parties will cut support for it. No matter how big the Switch's unit base will be, no developer will go through the trouble of downgrading hardware-intensive games meant to be played on future consoles (PS4 Pro, Xbox One X) for that long. Please keep in mind that, during its first year, the Wii U got ports of titles of the calibre of Mass Effect 3, Deus Ex: Human Revolution and Splinter Cell before being left to its doom.
What will keep the Switch alive in a year or two, at just half of its lifetime, will be indie games, first-parties and third-party exclusives (similar to what Bayonetta 2 was to the Wii U), which will only be pumped out if the Switch keeps selling as it is. I guess only Christmas will tell. If you want further proof about this uncertainty, which Nintendo itself shares, I'm sure, is the 3DS's support. They have claimed new games will still be produced throughout 2018, which is insane for a handheld console, considering they've also recently announced a new 2DS model. Why would you do that if you truly considered the Switch to be a worthy successor to both the Wii U and the 3DS (given its hybrid nature), with steady enough sales to support the company on its own?
I think it all boils down to your relationship with Nintendo first-party IPs: if you like them, you'll get hordes of them, and you can stay sure they will be high quality; if you don't, however, I'd be very wary, because third-party support could drop at any time in the next year(s, hopefully).