Thank you for doing what I asked. I am pleased. But how come I didn't hear it from inside the rabbit hole? Come inside, it's full of dirt.

I think they were pretty confident it's going to be a successful system (somewhere on par with the 3DS), as they clearly designed it with everyone in mind, but I don't think they knew that it's going to be that huge. Apart from the most optimistic optimists, no one was betting on 100M+ figures.

Nintendo spend heavy on market research so they knew what they were doing

Well the poll-option that would've been the best isn't there; Nintendo was in control the whole time, but did not know the Switch would be huge. This is obvious because nobody can know with certainty how well something will be received, even when you're making sure you make a solid product, which Nintendo did.

That was a nice fanfiction to read

They knew it was going to be a success. Switch Lite was likely the original hardware, they must have started planning and designing it as soon as the 3DS was released but their plans changed drastically after Wii U bombed 

Lite being released as early as 2019 severely indicate it was planned to be released just after the launch. If hybrid wasn't a selling point they would rush Lite release for 2018 and selling at 200 USD any problem with price would be solved because this was a proper handheld and Nintendo handhelds are successful, period 

At worst Switch hybrid was destined to sell some times better than Wii U as Switch wasn't going to experience a short life span and the userbase, even if buying mostly for playing handhelds, would still buying the hybrid version. Is the worst case scenario Lite would outsell the hybrid eventually, but Switch family would hardly sell much worse than the 3DS

Of course what happened was the exact opposite, the hybrid nature was the main selling point fairly outplaying their brand and market domination with portable devices. I can't say this surprised Nintendo, at best we can say they were not sure about how the market would receive an hybrid as it was a risk with no precedence, but I guess after some months of 2017 adopters data they already knew Switch was going to be a massive success 

Yes, they new.

I suspect that, at minimum, they were sure it would do better than the Wii U. I think the fact it really exploded was something they could see happen, were happy it did, but weren't betting the farm on it like how the PS3, for example, had a lot of executives being very 'YOU WON'T BE ABLE TO FIND IT IT WILL BE SO BIG' about it.

Nintendo put all of its eggs in one basket with the Switch. I doubt anyone thought it would be the juggernaut that it is, but Nintendo absolutely wasn't going to let it flop around like Magikarp. In previous generations, Nintendo was often spread thin supporting two-to-four consoles at any given time, and something always had to get the short end of the stick. Now Nintendo can focus on supporting and marketing one console, a console that plays to its strengths as a handheld while happening to have a TV out and external controller support.

To answer the question in the title, yes, the Switch was Nintendo swinging for the fences. Everyone has their own definition of failure and success, but the Switch was never going to be allowed to be allowed to be the former, all the way from the planning stages to post launch.

I think a bit of both. They wanted to try more after the failure of the Wii U and the 3DS performing far worse than the DS. But I'm sure they also knew what they were doing was somewhat of a gamble. The Switch is pretty much the first of its kind and Nintendo was taking some risks.