No I think you’re right that privileged access might not be a good idea (since any automatic refresh could pretty much completely take over the user’s system?) And actually there are upsides to the approach you’re suggesting - different desktop environments would have completely separate applications and defaults - when you install Plasma you won’t have GNOME apps cluttering your menus!
Having said that, it would be really good if one could use snaps inside the Plasma snap… is it possible to have a separate snapd instance running inside the snap? Perhaps with the parallel installs feature?