WebView support and PWA support largely both depend on the same set of functionality (disregarding Cordova/PhoneGap).

If Apple decides to arbitrarily disable some functionality in PWAs but not in-app WebViews then they're going to have a hard-time defending that, as all new web-standards specifications are built around privacy in-mind (as that seems to be Apple's overriding reason for not implementing some web-standard specification that benefits PWAs).