As soon as WebAssembly is stable and available I'm predicting we'll see a dramatic shift away HTML + JS as the target for most web apps. I don't mean blogs, I mean people who are trying to build websites that work like apps.

Most webpages today that would work fine in HTML 3.1 aren't built as massive JS web apps. If they are, it may serve a purpose (better UI/UX for most of their users being a major one.)