The Switch Operating system already has the necessary hooks to profile different performance modes.
The Switch 2 should in theory could just be additions to that scheme...
Hopefully Nintendo does a Microsoft and Sony and takes the current Operating system and builds upon it, rather than throw everything out and start from scratch, because that is what will determine the course of action Nintendo will take.
In saying that, if Nintendo builds upon the current software base, then developers should still be able to access the current Switch profiles to build games for in order to optimize for battery life on newer Switch hardware at the expense of performance.
Backwards compatibility however is not guaranteed, there are some big ISA changes between Maxwell and Ampere and some big changes between A57 and A78, it depends if Nintendo can be bothered to abstract the hardware enough, or if it's even possible.
--::{PC Gaming Master Race}::--
