Yeah I'm gonna go with 2023.

They'd be stupid to replace it any sooner frankly, with how brilliantly it's selling. It'll cruise passed 100 million if they don't foolishly cut it short.

Hell, 3DS got 6 years before replacement and it was far more outdated than the Switch. 

Probably 2022, no later than 2023

The majority of AAA PS/XB games dont come to Switch as it is so this is a very minor issue. Most of Switch's 3rd party support consists of indies, Japanese games, kid/family titles, previous gen ports/remasters, retro compilations & small-mid level current gen games. There are a few expectations but for the most part PS5/XB4 shouldn't affect Switch support.

Pretty much this, I simply don't understand the whole "Switch will fall off a cliff once PS5 arrives" thing. Sales trends show Switch and PS aren't really impacting each other directly; Switch's rise did not cut the legs off the PS4, and PS5 similarly won't cut Switch short.

It's already not getting the big Western AAA games so that won't make any difference.

2023, here's why.

They will release some kind of power upgrade, probably in 2020. That will give the Switch a longer life. Plus, Nintendo tends to have a 5-6 year life cycle in between one platform to the next. With how successful the Switch is, it will be in the 6+ years category.

They also need time for a lot of successful Switch games to get sequels on Switch. Super Mario Odyssey 2, Breath of the Wild 2, Super Mario Party 2, Mario Kart 9 (sequel to a game that was ported to Switch anyway), Splatoon 3, etc.  I think we'll get the next Smash in 2024 for the 25th anniversary, but that would thus be on the Switch's successor.

The 2023 release date would probably be March (Switch release month) or November (the industry norm).

Eh, while I do expect we'll get a second 3D Mario on Switch, (at least I damn well hope so)  I reckon the next mainline Zelda will be cross-gen like BOTW and Twilight Princess, and that they'll save Kart 9 and Splatoon 3 for Switch's successor.

2023

Six years seems pretty standard nowadays if the console is successful, which Switch obviously is.  Sony also follows the same trend which is why I still expect PS5 to released this year or at the latest the first half of 2020.  Six years.

That depends on the route Nintendo goes with the Switch. If they follow the trend of constantly evolving mobile tech, I could see them doing incremental upgrades while adding new features to new models to keep the concept fresh. They would do something like the NEW 3DS where some games would be the higher end version only, while most would still work on both. Then when the Switch 3 comes out, 2 becomes the new low end and the current Switch is phased out. If they did something like that, I would say as soon as 2020 we could see a "successor" to the Switch.

Now if the follow conventional console cycles, I would say 2022 is a safe bet. Nintendo almost always follows a 5 year cycle and at this time the PS5 and NextBox would be entering full swing, and Nintendo will want to close that power gap for 3rd parties at that point. The current Switch could still be supported through cross gen releases of less demanding games for a few more years though.

I'm hoping at least 2024. Not so much because I don't want to buy new hardware, but rather because Nintendo is kind of stuck between generations.

They need to start eating away at that and try to realign their launches close to Sony and Microsoft.

I expect by 2024 the portable mode should be capable of doing PS4 pro specs and have a decent battery. It will also give them time to work on the cradle/dock whatever you want to call it, to be able to host additional power in it to boost it significantly in docked mode. Docked mode will need to be within a couple tflops of the next gen home console in order to get simultaneous releases.

Then eventually after two more gens or so Nintendo should have been able to catch up for docked mode in terms of power and handheld mode to be perhaps 75% of previous gen's console ability.

They have the proper architecture for it this generation. Why not until after next generation?