It's like writing an entire diatribe about how it sucks that people can insult you online, and how that should change ... and not even mentioning the benefits of freedom of speech.
They'll make you a minister in the UK for that.
I don't think what the author is talking about is necessarily against either. HTML5 can continue its evolutions while "HTML6" (or something completely separate) exists alongside the traditional DOM, like the <canvas> example they reference or like WASM exists alongside JS. From this perspective, the article is about why it's a worthwhile time to make the new thing rather than why the new thing won't also have baggage in 20 years or why we should just throw everything current out the window as part of supporting the new thing.