Unless they switch to a much more powerful console (and possibly keep an optional handheld) I don’t really see much use for a new Switch. I would really like to see them compete with PlayStation and Xbox again by being able to support more games that run on those consoles. I think that would immediately create a much larger market for Nintendo. At the moment, Nintendo is mainly doing its own thing with many of its own brands and otherwise undemanding indi games.
I don’t really get the impression that they will make much graphical progress with their own titles for the time being, it is also the graphical style of many Nintendo games that does not require anything special anymore.
Apart from the fact that they may want to support higher resolutions, a larger screen and more frames, I can’t really imagine what is expected of a Switch 2.