Oh, this one will take a while alright. Since it's TDP restricted it depends entirely on node improvements and these are trending more and more spaced over time, specially power consumption wise. On the plus side, they're using Nvidia. I'm thinking late 2023 at the very least, and probably 2024.

2022, having complete backwards compatibility with an iterative successor will mean there is no reason to prolong anything. It'll mean a smooth transition to simple more powerful hybrid that will allow for 2022 games to run acceptably on the handheld/home console at the same $299 price.

Depends on what you consider a successor. I think we could have a “Switch Pro” utilizing a more advanced Tegra processor as early as 2020. As for an outright Switch 2/Switch successor, that operates on way more advanced tech, changes the form factor in a way that hurts joycon compatibility, etc, it could be as late as 2025.

Personally, I’d consider the Pro a successor, so I’ll vote for 2021.

Don't get me wrong, I'd love it if we got a BOTW successor for the Switch in like 2020, but given the huge success of Twilight Princess and BOTW going cross gen and the fact that the last 2 mainline Zeldas have taken 5+ years to come out, I don't see BOTW's successor arriving before Switch's replacement.

What you describe sounds more like a New 3DS/PS4 Pro/Xbox One X type revision. Do you consider those successors to the 3DS/PS4/Xbone?

A leaker on Resetera with a pretty good recent track record has stated 2020 will have something BOTW related. That's kind of vague but they seem to be pointing towards a sequel.

I'd be over the flipping moon if we got a (worthy) BOTW sequel in 2020. I guess after the incredibly drawn out production cycles of Skyward Sword and BOTW I've just been conditioned to expecting Zelda to take forever haha.

Keep in mind to I think the main development of BOTW was probably done late 2016. So by early next year the game will have been done for like 3 1/4 - 3 1/2 years. 

I still think we'll get one in 2021 rather than 2020 though. 

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.

I'm assuming it's a Majora's Mask style sequel that reuses the engine & assets, possibly even the same map rather than a full blown everything from the ground up type of game.

Ugh, don't think I'd buy that tbh. I know BOTW's map too well, I want a new world to explore.