If Wii U can get 4.5 years, Switch will get longer than that. So all of 2018, 19, 20, 21, at a minimum. If I had to guess, to keep up with the other consoles, they'll cut it off after a bit over 6 years (not completely obviously, since Switch still exists even with a successor around just as 3DS still exists today). So 2022, plus most of 2017 and at least some of 2023 would make 6 years. I'd say Switch successor releases in late 2023, early 2024 then. That gives just enough time for Metroid Prime 4 to still release on it and have a couple years to get some sales.
Edit: To clarify what I mean by keeping up with the other consoles, I'm of the mind that while Nintendo doesn't compete with Sony and Microsoft directly, they still are interested in expanding their third party offerings. To appeal to the Bethesda, Ubisoft, and EA ports of the world, they have to maintain a similar dynamic between their hybrid and the home consoles to please the publishers. The customers obviously could care less if Switch matches the other current gen consoles in might, but I do think having a console close enough to XBO and PS4 as Switch is eases some of the perceived risk in publishers minds on releasing ports. It won't ever earn Nintendo the latest bleeding edge graphics games on their system, but I think it got us Crash, and that's enough for me. I think Nintendo feels that was worth it as well. There's also the issue of being able to run the latest game engines. Even indies care about that to a degree, and it's even been useful for 1st party titles as well, as we've seen with Yoshi running 60 fps on...Unreal 4 I believe it was? If Nintendo's own in-house developers are getting use out of it, I'll bet that they'll start to prioritize getting them on their systems, and won't allow themselves to fall too far behind on that front.
Last edited by HylianSwordsman - on 27 February 2019
