Goalposts move, definitions change... but if "progressive" doesn't refer to the progression from HTML to elaborate UI in JS or mobile, does it still refer to the movement from simple to more complex? Or has "progressive" become a great sounding word, like "agile", that everyone wants to claim? Nobody wants to describe themselves as lumbering and clunky instead of agile, or regressive and backward instead of progressive.
ETA here: The missing idea here being that when using these OS-specific components, you should do it in a progressive enhancement way such that they have fallbacks or offer alternative functionality when they don't exist. Try to avoid the old west days of "Works Best on This Particular Browser/OS Combo".
There is definitely a need to preserve the old meaning of "progressive enhancement", but that may be a need for a new term, as this one moves on. Particularly the more that it feels that JS has "won" and is the default much more than the exception. I used "artisanal" as a joke in the previous post, but it's also somewhat apt here as raw, barely filtered, HTML [1] feels increasingly like a fad for hipsters and old curmudgeons more than the way of the web. To support it as a movement you might have to market it in similar "return to the web's roots" marketing.
[1] Just like Grandma used to bake.
Progressive Enhancement is an important aspect of PWAs, as it is for web development in general. PWAs are bringing new features to the Web, but it should/must be done in a way that does not break the experience for anyone else. I guess that's why Alex chose that word in particular.
In the specific context of PWA, I've seen progressive enhancement is most often specific to how the app-like enhancements are applied (ie, use platform notifications if they are available, fallback to something like a JS toast library, if not), not necessarily to, say, the relationship of the HTML and JS. Many PWAs in the wild are still SPAs (and still going to be SPAs), and arguably a SPA is going to provide the most app-like feel for a PWA on a user's device, rather than something "pure" and HTML page driven.