What you're describing is not progressive enhancement. It's a mental exercise in re-implementing a website with workflows designed for heavy JavaScript usage without using JavaScripts. Which is silly.

For example, if you ever tried PE for real you would know that there is no point in implementing collapsible comments in pure HTML. That's exactly the kind of functionality you "enhance" via JavaScript. Of course, like most modern developers you've never really tried the practice, so you don't have any experience with such things.