The Switch is lucky in that it will probably get until late 2020 or so before it has to deal with the next gen Sony/Microsoft competitors. By that point, it will have sold a ton, so even if the next gen competitors do hurt it, it will still be a hugely successful system for Nintendo and they can plan the successor to launch in late 2022 or something if next gen systems really affect it. 

Hmm, are you suggesting Nintendo would make a next gen home console only and continue to use Switch as their portable? Really can't see Nintendo ever returning to strictly home consoles. Its too risky for them. I think the hybrid concept is here to stay for them as far as home consoles go. Now in terms of portables, I could see a small chance of a 3ds successor happening.

I think many people assume the next iteration of the Switch will use an off the shelf Tegra but my bet is that Nvidia is hard at work on a custom design for the next version. The Switch has been a very big mover for Nvidia mobile chip segment so my guess is that they probably will go back to the drawing board and come up with a design that's beneficial to both the Ai self driving segment and the Switch gaming devices.

A 3DS successor while the Switch is a thing is not happening.  No real point TBH when they can just selling dockless SKUs.

I am not saying going strickly console will not be a risk, but Nintendo is known for taking risks.

Motion Controls was a risk.

Tablet controls was a risk (that did not pan out).

Virtual Boy was a risk.

Hell even the Switch was a risk as many, investors included, thought it would flop.

Now that does not mean they will take the risk.  As I said, a Switch Pro, or NEW Switch is still totally an option.  However if they do not do one of those two things, they will be relying on 3rd parties to either make Switch focused games or lose support completely...which is a huge in of itself.

I feel like not taking a risk and capitalizing on the traction the brand had started gaining would not be in their best interest.  At the very least, a Switch 2 would have to land by 2022 after a 5 year cycle.  But even people would still need to be willing to get 3rd party leftovers because they would likely be in the same boat they are in now as support (not horrible, but not great either).

Switch is their meal ticket, of course they will say that. But we all know it's not the truth. Switch is not really driving third parties crazy as it is and things will get worse in the near future. Let's just accept the fact that it's not powerful enough and that Nintendo's relationship with most publishers is not the best.

Why would things get worse? The system is already getting Japanese devs and indies on board along with a smaller selection of Western third-parties. Moreover, as the install base increases, there should be more games coming from third-parties. I don't believe many here expected a tablet to be able to get even the plurality of the big cinematic AAA multipats, but those are not the only games being made by third-parties.

The thing you're forgetting is next gen starts at 0 while NS will already have 30m+ head start at that point, it took developers 2 years to finally leave behind the PS3 and 360 and start ground up games as well not to mention Switch has an entire market to itself (one that means it has Japan locked down) and the dynamic of the industry.

Many type of games by admission of developers themselves are simply not suited for the PS and Xbox platform's ecosystem anymore (think games like TWEWY and such) they do however suit the Switch platform fine and developers as each gen passes find it harder to ignore the potential for money to be made.

If Nintendo's successful devices relied on heavy western 3rd party support, I'd be concerned for the Switch's future. But since the best selling titles on Nintendo platforms are historically:

A.) Nintendo 1st Party Games

B.) Japanese 3rd Party Games

and

C.) Indie Games

I feel Nintendo will have it's own little niche area to itself. I don't need my Switch to be a PS5. I'm excited to see what developers get out of it as the console is very young. Square Enix has created a specific division just for Switch titles, Level 5 said all their upcoming games will be made with Switch in mind, Sega, Capcom, etc. have to support it in Japan by default. It'll be fine.

Now, would it be nice to have day and date AAA western 3rd party games on Switch? Hell yeah, but it's not part of Nintendo's successful DNA, for the most part. I see the Switch performing like the SNES, DS, Gameboy and 3DS. It'll continue to get great 1st party support from their rich library of IP, Japanese 3rd parties will make software to appeal to the Switch as it is dominating in Japan, and indie titles continue to sell the best on the Switch, even more than others combined. And that's fine because those platforms seem to favor more western styled, AAA games. I feel Nintendo just needs to focus on pleasing their largest demographic.

A lot of people may not see it now, but I think Switch, even in the midst of PS5 and Xbox 2 will have a bright future. It probably wont' get many next gen games at all, but it will get enough support because the device is selling well.

Basically any type of small-medium sized title (A-AA) is well suited for Switch, this includes

1. Indie games

2. Japanese games

3. Kid/family games

4. Last gen remasters

5. Retro compilations

6. Mobile conversions

7. Free to play games

8. Late PS4/XBO downports

These are currently the type of games Switch gets and for the most part they seem to be performing pretty decently and despite what some people are saying, the release of PS5/XB4 will have little affect on this type of support.

People need to realize that Switch is the successor to Wii U, 3DS and in a way Vita so we should be looking at it receiving the consolidated support of those devices.

Did the DS stop selling when PS3 and 360 came out?

Did the 3DS stop selling when PS4/Xbone came out?

The Switch does not depend on AAA third party games or being graphically competitive drive sales, so PS5/Nextbox won't really affect it. The only thing that can derail the Switch now is if Nintendo themselves fail to maintain its momentum with price cuts, hardware revisions, and killer app software.