I want to bring up a serious topic.
What if the Switch fails? And how can that happen?
If it fails, I think Nintendo will honestly just leave hardware development, if not video games in general.
No, that's not a "NINTENDO IS DOOMED" theory. Nintendo is a business. They made toys, cards, and love hotels before video games. If they continuously fail in the hardware market (i.e twice in a row, which is enough for investors to start pulling out), then they will see it as a non-viable market for their talents, and they will move on from it. They still have plenty of other avenues they could pursue and possibly have a much greater focus on, such as movies, toys, the theme parks, mobile gaming, etc. They have a lot of money in the bank so they could definitely break into more profitable markets and focus on them should video games stop being viable for them.
Ways in which the Switch could fail, would probably be a combination of these things:
-Consistently poor stock at launch, or beyond. Nintendo is known to try to limit stock intentionally in order to create artificial hype and demand (amiibo and NES Classic being the two most notable examples in recent times). It's a dangerous tactic and it seems like they are doing it again. I wish they'd stop doing it as I think it doesn't actually do anything for them, and only makes consumers mad. We'll see how it works out.
-Not being able to keep up a consistent release schedule of solid games that consumers are interested in. I do think Switch will have a good launch line-up, but we can't soundly predict much past the first three months or so.
-How well they can convert the Wii U fanbase. It may not seem like a big deal, but I think this is important. While they could very well make up the minority of hardware sales, especially if the Switch is a big hit, the fact remains that the majority of Wii U owners were basically actual, big Nintendo fans. I don't want to say "diehards" because not everyone is, but they're the people that have a specific interest in Nintendo beyond the times where they happen to be in the limelight (like with the Wii). As a result, I think the Wii U fanbase would provide the majority of software sales on Switch if they can convert most of them over. So I think relying TOO much on Switch ports of Wii U games would be to their detriment, especially if they aren't spaced out. With the exception of Smash and Mario Kart, I think most Wii U owners aren't actually gonna "count" them as real titles, unless they have a lot of new content. I also think Nintendo should try to give Wii U owners some kind of reward for sticking with them, like discounts on Switch ports if they have a Wii U game tied to their NNID, but I am not sure how feasible this is.
-Battery life. I could be being a bit dramatic, but I think the system lives or dies on this alone. The main draw of the system is being able to play home console quality experiences anywhere, but if you only get like, 3 hours battery life out of it, people are gonna lose interest fast. So they need to make sure they have this bit right. IMO, I think 4 hours on max level settings, and 6 hours with power saving settings, would be a pretty acceptable range. Basically, it can't run out of battery as fast as the Wii U GamePad.
-Unfortunate coincidences that are out of Nintendo's control. Some things happen, like people just not having money for it when it comes or not seeing the ads or whatever, and it's not necessarily anyone's fault. The former is also why I won't buy it launch day, unless they have like a Rosalina game or something.
It's also worth noting that I think Switch will replace the 3DS within a year, and Switch will be the sole platform for Nintendo's core video games. So they don't really have a handheld to fall back on like they did with the Wii U (though it might be for the better).