You have to look at releasing a new system as demanding a purpose and serving a need. For the foreseeable future, thanks to the architectures chosen, Sony, Microsoft, and Nintendo can continue with the iterative system updates of the PS4, Xbox One, and Switch, rather than establishing a whole new system.
Again, there's nothing unusual or extraordinary about this idea, it's just that consoles are finally following the precedent already set - successfully I might add - by PC and mobile. It's the modern way of doing things, and, frankly, until there's a reason to be concerned about it (like hitting up against a technological limitation of some type), something to get behind. It's kind of silly to have to start over from scratch if you don't have to.
Nintendo is the one I doubt would go about it this way the most. Nintendo has always done iterative upgrades within their handheld lines with backwards compatibility but didn't force developers to make the games work on past handhelds. Game Boy games can run on the Game Boy Advance but Game Boy Advance games can't run on the Game Boy. DS games can run on the New 3DS but New 3DS games can't run on the DS. I bet the Switch line would be the same. Nintendo already has problems with third party developers and adding extra requirements like not allowing them to push the new specs because they have to support a Switch four iterations back wouldn't be helping matters. Nintendo also needs the specs to be pushed to keep their distance away from phone/tablet games because mobile developers are under no obligation to support the very first Android phone or first version of Android and, therefore, mobile games would start to surpass Switch games once the average phone/tablet has higher specs than the original Switch. Also, them allowing developers to push the specs would allow Nintendo to catch up to Sony and Microsoft.
Just four days after Nintendo released the Switch Nvidia revealed the Jetson TX2 that has 2X the performance or 2X the energy efficiency of the X1 in the Switch and it all fits in the size of a credit card:
It is very likely that this or a version of it will be in the Switch 2. When that happens I think it is very likely that it would be backwards compatible with the Switch 1 while taking advantage of the 2X the energy efficiency part by BOTW lasting 6 hours instead of 3 and doubling the battery life of all the other original games. But the Switch 2 games would take advantage of the 2X performance part to get the new games closer to the other two console manufacturers' consoles while distancing the games more away from phones/tablets that are starting to catch up to the original Switch. They may also switch it around to make the backwards compatibility performance better. For an example, if the Switch 2 has a 1080p screen then it may use some of the extra performance to treat Switch 1 games as if they are in docked mode while in handheld mode. In other words, I think it is very likely that Nintendo would continue to do what they sometimes do with their home consoles but always do with their handhelds by maintaining backwards compatibility but allowing the new games to take full advantage of the new specs. To do otherwise would be like Nintendo asking developers of new games for the Switch 4 to also make those games like retro homebrew games for the Switch 1 while supporting all the handheld and dock modes for each iteration all the way down. That would be asking more from developers than if they asked them to make sure that New 3DS games run on the original DS which they don't do and have no reason to.