I would consider being able to install the app to the homescreen part of having a "native app-like user experience". And installing to homescreen is listed as part of PWA on that MDN page.
There's some more relevant discussion on this bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=1407202
For now you can supply --ssb on the command line - but I suppose that will go away, if the feature discussed in op is axed (it's not entirely clear to me if axing the pefrence/feature flag includes axing the command line flag - but it seems so).
At any rate - most desktop os' should allow shortcuts to urls - so should support "installing" apps.
That's just part of it though. What about hiding browser chrome, or making sure it opens as a new window instead of a new tab, or having seperate window preferences (such as size and location) for it? And I believe one goal of PWA is that "installed" apps have additional permissions, such as being able to use keyboard shortcuts that are normally reserved.
Pretty much: Have a Service Worker and/or a Web Manifest and you are well on your way to claim to have a PWA