So I know that Pokemon ALWAYS supports a system pretty late into it's life but I want to mention one thing. The announcement of Pokemon Legends is EXACTLY the kind of thing that is indicative of WHY it's reasonable to believe Switch will have a long life ahead of it. I know that Pokemon can kind of be an outlier because we saw things like Pokemon Black and White 2 releasing a year after the 3DS but I think it speaks volumes that in the era of HD development we'll probably (and this is speculation, so don't be too harsh if it ends up being untrue) be seeing 3 Gamefreak-made ORIGINAL games. The only other time this happened was with the DS, which to be fair did not have a super long life or anything, but that was also in an era where games took less long to make.
To be clear, I'm not saying "Switch will definitely last long because Gamefreak is an indicator". More like, the fact that we'll have 3 brand new 3D Pokemon games (instead of 2 gens, a remake or two, and a third version) along with titles like Splatoon 3 being announced is probably indicative of the fact that Switch will be consistently selling enough for Nintendo not to want to abandon ship too early.