Aside from File Access, I haven't seen any of these. PWA is sometimes mentioned on HN but I've never seen one in the wild (I had to look up the term a few weeks ago). Worklets, WebComponents, and Houdini, I never heard of. I'm not the most in the loop person since I'm not a web developer, but you'd think the cool stuff gets at least mentioned, so going with that, the most recent progressive feature that comes to mind is still the PDF reader (other than general maintenance work to keep up with HTML5, which all browsers do, and which I assume MSIE was also doing in the 4 year period mentioned -- or CSS3 or whatever was hot back then).