Wow, we still have people who think Nintendo needs ports of PS/XB games to sell hardware?

A much more portable console with smaller screen and maybe 1080p resolution and running at the docked performance level while portable. More flash memory and much lower price. They simply move the Switch into a true portable position similar to 3DS and DS. Docked may become less important and we may not even see weak versions of ps4 and xbone games it will simply rely on games written exclusively for the Switch like 3DS. Nintendo will have to react to what is available though. Android devices are getting more powerful all the time and are already not that far from Switch. I saw that the iphone 8 plus in one benchmark (GFX open cl) scored something like 6,700 compared to about 3,300 for the Shield box which runs the Tegra X1 at full speed, slightly faster for GPU and almost double for CPU compared to Switch (although 1GB less memory) and mobile chipsets rapidly improve so will the Switch be viable when people's phones and tablets are much more powerful for far less money with a wide range of much cheaper albeit inferior playability generally games. Consumers really will dictate how long the Switch is viable. In 3 years time the Switch may have difficulty selling. I'm not saying it will but its possible. Nintendo will monitor sales and analyse them to work out when they need to release a new console. If Nintendo are forced into heavy discounting to shift consoles I suspect they will be more than keen to bring out something new.

It's true that it's usually the least powerful console that sells the most, but it's also true that it's usually the console (s) that have the best games that sell really well or even sell the best. 
It was that way for NES, SNES, PS1, PS2, Wii was an exception, although PS3 and XB360 sold really, really well, and PS4.
Nintendo's handhelds never really had competition until the PSP. And what happened? DS. An exception.

The problem with having, in this context, a console (Switch) that can't play a great amount of games (on PS5 and XB1) will mean, again, that Switch is a console for Nintendo games - and Indies.
In a normal situation, how many times did Nintendo sell really well or the best, without the best 3rd party games? Switch might be the first. And assuming that happens, the novelty of portability might not work for Switch 2. And then what?

Switch is being sold as home console that you can take it on the go; People have embraced that perception; It's games are home console games.

When PS5 and XB4 arrive, assuming we still have the original Switch or a marginal increase in power with a Switch 2.0, people WILL compare it to home consoles.

If they go with just portability they will be "selling" an inferior product and they will basically kill what made Switch a hit.

Right cause Switch isn't making records while being underpowered against 4k gaming while being 720p/1080p... It Doesn't Even Have the Price argument cause It's more expensive then some PS4/XBOX deals.

When Next Gen arrives, It will atleast have a killer lineup and pricing and probably a revision.

At this point, Power isnt that Important. Its not like The Wii vs PS360 problem where the Wii wasn't HD in an age when it was everywhere. 4k will never have even a slice of that impact.

Also, Switch Is now being sold as 1 per Person and not 1 per Home. Which signal a more portable device...

Its barely getting any ports of PS4/XBO games now so i have no idea why people think it needs PS5/XB4 ports to be successful.

That's a logical move. Over time it can be improved via hardware upgrades. In three years or whatever. At that point Switch will be $200 or slightly less.

On tegra? Oh dear, there goes all third party when PS5 releases.

Yes, Switch is doing very well, but what's helping it won't last forever.
So far it is and people want a Switch for that and of course, Zelda, Mario, MK 8D, etc, the same way they wanted motion gaming.

Both portability and 1st year line-up's effect won't last forever.
When PS5 and XB4 arrive, they will be the new consoles full of possibilities, new experiences in the years to come. And either Switch has what it takes to fight them in their promises, novelty and shiny new graphics or it will suffer.

The power gap might be big enough to make devs decide to focus their resources on the new machines instead of wasting them to port to Switch - or try to.

We can see it having a good library filled with Nintendo games, but good enough to fight new consoles, when most of Nintendo's games already reached most of it's potential consumers?...
Pricing is no longer a big factor to decide if transition will happen slower or faster. People bought the PS4 in droves despite the 400$ price tag.

Power is not a selling factor, per se, but it really is a great marketing tool! And at the end of they day, perception probably sells as many consoles as the actual games.
Also, have you forgotten how much criticismo XB1 got because the version it got of quite a few games weren't on par with the PS4 version?
And for devs, power makes all the difference.

"Also, Switch Is now being sold as 1 per Person and not 1 per Home. Which signal a more portable device..."
That's due to it's nature not the fact that it's being  sold and perceived as a portable. It's the opposite.

I see them releasing a sequel quite soon but I think they will support 2 platforms simultaneously. All first part games and 90% of Japanese support will be cross-platform with the Switch/Switch 2. But Switch 2 will obviously be the place to play any western games and superior versions of all other games.

Well if the 3DS can reach 80 millions with a 240p screen and a public that never really hyped it up much, Switch can certainly do better cause it's already attracting a bigger and more wide audience than the 3DS.

3DS has barely any support going on from Nintendo and third party but is still up from 2016 lol. So in the worst case scenario, which won't happen since 3DS was being contrained by a second system and Switch launched, the Switch would still be able to survive.