Irrelevant? You think third party software publishers see them as irrelevant? If you do then honestly, let me just laugh directly at you. Because you'd be so naive that I couldn't help myself from laughing. The success of third party titles on PS4, whether or not they are available on the Switch, is why it will continue to get more third party titles. The PS4 is an ecosystem where there the audience has many different tastes and are not completely focused on one sole publisher. That is its huge advantage when it comes to third party software. When or if the Switch reaches that point, when large-scale projects such as Yokai Watch aren't abject sales failures, then there would at least a starting point to discuss whether or not the Switch will overtake the PS4 in terms of third party coverage. 

It's irrelevant to the comparison because there's no way, at all, of knowing what those would do if they WERE on Switch because they are not.  It supports why the PS4 would continue to get support, absolutely.  But that is not the same as the Switch not getting it.  The question isn't one of dropping PS4 for Switch, but doing it in addition to PS4.  The fact you are acting like it is a zero sum game is the only truly laughable thing here.

Also, YW4 is continuing a sharp downward trajectory that began before the Switch that is driven primarily by absolutely terrible IP mismanagement, which you can read multiple articles on if you wish.  And others and myself have listed off multiple strong performers on Switch from third parties.  So please do tell, how many does the Switch need for the discussion to start, hmm?   Because from where I stand, the discussion has been worth having for a while now. 

The larger issue I see is a lot of these Japanese devs either A) see the Switch as a place to do cheap cash ins until they can't get away with it anymore (Capcom mostly) or B) insist on doing late ports flr whatever reason, most likely because they think doing so will get them both new customers AND double dippers.  Third parties need to build their audience on Switch, this is true and it will take some time.  But several of these companies NEED to do it.  Not the biggest juggernauts but the mid teir ones.  Because a lot of them got nice sales from the Vita or 3DS and those ecosystems are completely dead.  They need to broaden their audience and to do that they need to start releasing good versions of their games on Switch *concurrently* with the PS4 versions and actually promote them worth a crap.

A Switch plus in line with the New 3DS, that I could see for 2021. But a successor to the Switch? Certainly not, way too early for that.

Everyone believes that he wants. Switch Pro or Plus or whatever is coming soon with only sperficial improvement, not the one of August, but I believe that soon (first half 2020) we get a 1080p screen with some unlocking of the Tegra X1, but no way this thing can run PS5/scarlet games like ReviewTechUSA alaways repeat.

And yes, in 2022 we get a new 9th gen console which will have a different name.

Thing is, it doesn't have to. As long as PS4/XBO will get supported with ports, there's no reason why they don't make a Switch version out of those, too. Sports games will get ports for a long time anyway - just look at the PS2.

Hence why I highly doubt there will be a Switch successor in 2022 already. There's simply no reason to kill off the Switch by that point already unless Sony or Microsoft (or somebody else, like Sega) brings out a new handheld console, which would force Nintendo to react to that (like they did with the DS against the PSP and the 3DS against the Vita).

It doesn't even need that; it could live on just fine on indies, exclusives like Octopath and Astral Chain, ports of older games, and first party. AAA blockbusters have never been the system's selling point so losing what few it has won't matter.

Of course. But having these too is always a good bonus. It helps if people don't have to buy another system for some games they love, but like you said, they're hardly a selling point.

Oh yeah, don't get me wrong, as a Switch owner it's nice to be able to play stuff like Doom, Wolfenstein II, and soon Witcher 3 on my system, it's just I doubt sales would be affected if games like that stopped.

I think they have an effect even if they aren't massive system sellers.  I think they help most with perceived value and keeping the console relevant in people's minds when Nintendo themselves can't provide a release a month.  This first half of 2019 I think shows that.  The only big new game from Nintendo was Yoshi until Mario Maker came out at the very end.  Yet, it has been up YoY by a considerable margin.  Some of that is no doubt Smash, but I think it's no coincidence that last year a similar situation resulted in a pronounced drop off while this year it sustained momentum nicely.  Mortal Kombat reportedly saw strong sales and multiple other ports, remasters, and new releases filled out the schedule.  These didn't lead to sales spikes, but they kept Switch relevant in the general consumer base's minds.  

Basically, the problem PS5 and Scarlet will bring is not taking away massive system sellers, but rather the loss of those games will result in Switch being left out of the headlines for prolonged periods.  PS5 and Scarlet will be the new hot thing and that will pull spotlight from the Switch.  This is why I feel a Pro model would indeed be wise.  It can encourage more ports, but more importantly it gets the Switch back to feeling more new fresh.

Those games that fill out the schedule don't have to be big current AAA blockbusters though, they can just as easily be stuff like Octopath or Cuphead.