PS5 & XB1 comes in 2020, at that point Switch probably stops getting multiplat 3rd party support.

You could be right, nintendo simply goes "we dont care anymore about it, we re riding this gen out without any support"
Hopefully by then, they have sold so many units that devs will want to keep makeing games for it reguardless.

I just assume by then (2021) nintendo will have launched a new console instead, rideing the coat tails of 3rd party multplats from the PS5/XB2.
People say nintendo switch is 9th gen, and their gen ahead.... it see it as them being behinde the others, and assume they would want to try and stick to the others atleast.

Around 8 years, with some revisions included, then switch 2, with a big step forward. There are potential improvements that are unlikely to be on a revision.

AAA support=/=3rd party support.

Look at the 3rd party support on Switch. It's mostly indies, Japanese games, previous gen ports/remasters, kid/family titles, retro compilations, mid sized free-to-play games.

The type of games you are talking about already dont come to Switch.

Exactly, next generation really isn't going to matter that much, especially since AAA games are going to require even more to make going into the 4k era. Diminishing returns is a real thing, and its effecting how developers approach game development. Even if the Switch doesn't get a lot of the AAA titles, it'll still have plenty of stuff to pull from in the form of exclusives, indie games, service titles, mid-budget games, retro re-releases, etc. That's more than enough for the Switch to serve as a good complimentary console to someone's main gaming system, especially since some of those games simply work better on the Switch than anywhere else. 

Honestly, i doubt Nintendo can ride the Switch and the Switch line for more years than usual if something doesn't change structurally.

Specs wise, it won't be able to get the best 3rd party support - as it hasn't been getting now. But the problem is that the absence and importance of such games has been overshadowed by the like of BoTW, Mario Odyssey, Splatoon 2, Mk8, Smash and Pokémon. But how many times can you deliver a game with the impact of Odyssey and BoTW?

This means that a few years from now, most of Nintendo's system sellers will already be out. And where's the support from 3rd parties to cover that "hole"?
Switch owners will either get less games or ports and more ports. So far, so good, but ports and more ports will eventually upset people.

And this is where i believe people won't be so forgiving as they are now.
As it is, people don't seem to care so much about this because the system sellers keep coming, but when that's pretty much over… the mentality will change too.

The portability factor is still relevant today and for some more time, but like everything, it will end up losing it's appeal.
So, i really hope that the Switch line, if it continues, offers something more.
The lack of apps (amazon something, netflix, etc.), better online services, will eventually be more visible. And needs to change.

I'm pretty sure Nintendo themselves have said they are aiming for a long life cycle for Switch.

Next generation isn't going to mean much. AAA games are already expensive and time consuming to make now, it'll get even worse going into next generation. This entire generation, publishers and developers have been relying on cheaper to produce products like Remasters and service titles to fill the gaps. Switch is already getting plenty of those, on top of indie games, exclusives, and mid-budget and Japanese titles from the other consoles. Switch was never going to go toe-to-toe with the other two systems, so I don't know why you were expecting otherwise. 

For Nintendo's system sellers, it's true most of them are out now. But they don't stop existing once they release. They're still strong enough to sell consoles even years after they launch. Plus, Nintendo can always move forward with new IPs, and other sequels to add to that list. Just because we got most of Nintendo's staples this early, doesn't mean the well has run dry. There's always plenty to do in game development. 

Portability worn't loose appeal either. It's not like Motion Controls for the Wii which can only be the selling point for so long, people will always want a device with games that sits between small phone apps and big console experiences. The Switch fills that gap expertly, and unless a direct rival pops up and steals its thunder, that appeal won't die anytime soon. 

nVidia's Autonomous machines/self driving cars initiative has pretty much imploded anyway.

Which means, nVidia will likely try and re-purpose Xavier for other markets to recoup R&D costs.

Well. That's just a blanketed statement. The partnership will last for however long Nintendo wants to keep it going, if nVidia doesn't have anything compelling, then Nintendo will likely walk away.

As for dropping in a new Tegra chip... There is only the Pascal derived Tegra that is a drop-in replacement to the current chip in the Switch, which would offer a big boost in performance at the same powerlevel.

The Peripherals are great. But the more mechanical action you have, the more points of failures you have.
For Nintendo it's unlikely to be an issue because they get to sell more kit... And hopefully the Joycons last the test of time.

Of course not. It's going to stick around as long as people keep buying it.

Resolution Gate when the Xbox One and Playstation 4 tells a little bit of a different story.

If you had an Xbox One X and a Switch sitting side-by-side, then the Switch's hardware will become readily apparent of how limiting it truly is... And that will influence some purchases. - The Switch's mobility will influence other purchasers... Not all consumers have the same need/want/desires as everyone else remember.

Shit. The PC has an entire community devoted to the quest of more power and more graphics... And another community devoted to making the latest games run on the crappiest of hardware, irregardless of visual fidelity.

Outside the Internet gaming forum bubble, most consumers really don't give a shit about having the latest and greatest hardware power in a console these days. There's still tons of people who are just fine with buying a base PS4/Xbox One over their Pro counterparts. I agree that there is still a market for high end gaming hardware, but the success of the Switch with both consumers and developers shows just how little hardware power actually matters these days in the grand scheme of things. 

Define "most". - Because there are 10's of Millions of PC gamers, Xbox One X owners and Playstation 4 Pro gamers that would probably disagree.

I am not denying a large percentage of gamers don't give a shit about visuals, I am just not willing to brush off those who don't fit into that category.