It seems like the ability to port next-gen games is up to the strength of the dev that does the port. A good example is the port of the Witcher 3 that is a generation ahead of the Switch in terms of graphical capabilities.
Another interesting item is the impact people are expecting from the new NVMe SSDs that are expected to hit the PS5 and XsX, and how this component and new data is strategies will allow the consoles to zap loading times and increase the amount of data available per frame. This kind of upgrade would be available in a hardware revision. Of course it would make the original Switch slow in comparison, but the upgrade could be optional in games depending on the HW revision you're playing on.
There was also a really interesting thread on NVidia's DLSS v2.0 and its increased fidelity in producing quality 1080 to 4k upscaling or even very good implementations for 520 to 1080, meaning that the hardware would be required to do less churning to produce comparable results. It also makes it that the game would be the same on a weaker and newer revision, but boosted with such a tech. https://gamrconnect.vgchartz.com/thread/242226/how-the-switch-2-could-do-4k120fps/1/
Then we also know that the next major graphical leap next gen is ray-tracing. The feature can already be turned on or off on games like minecraft, so similarly the new revision could pull off ray tracing, while leaving it off on the OG Switch.
That's as far as I can write to you, but the best way to look at it is to see how games are compatible across multiple builds in the world of PC gaming, so we can use that as a way to see what's possible in a multi-revision paradigm.
I don't think there will be anything on the PS5 that can't be ported to the next Switch, or even this Switch for that matter. But, the bigger the gap, the more difficult it will be.
As for the rest of the stuff, I'm too tech illiterate to understand anything beyond SSD.