This is just my opinion, but the extent of changes that I'd like to see in a Pathfinder 2.0 is a restructuring and reclassification of the fundamental rules on how things like combat work.
Like, you don't need to reboot the whole game to clean up the combat section so rules are better organized within the text. (And really, the fact that rules are all over the place isn't really Paizo's fault—they were largely copying WoTC style, and you can't blame them for wanting to keep things as samey as possible during a time where Paizo wasn't known for game publishing.)
To be honest, most of the frequent complaints revolve around a handful of spells and corner rule cases, and a few specific classes (such as the wizard and fighter). You could probably do everything that Alexander talks about, and clean up the those problem areas, and still leave the game intact enough that folks could play there favorite APG or OA class or use Bestiary 3 without a problem.