Why? By the time Switch 2 releases, those systems will be a decade old. Mobile technology will have adanced a long way since then, along with the techniques for creating games.
I'm expecting Switch 2 to actually be far more optimised with switching between 1080p portable, and somewhere between 1440p-1800p docked. After having one long generation with Switch under their belt, they should be more prepared and comfortable with the tehnology and concept.
Personally, I wouldn't even mind if the next one were to continue doing 720p portable and 1080p docked. What I want them to do with the extra power is just make prettier games and make games run better, especially for third-parties - it's amazing how crappy third-party games can run on the Switch, even games that theoretically wouldn't need much power. I know that's a porting issue more than the hardware itself, but for one good example, there are a lot of UE4 games that run like crap on the Switch because optimizing them takes too much effort. I want that sort of thing to be better.
Though yeah, for the general gaming market, it'd probably look really bad if they released a 1080p console well into the 2020's.