Things will steadily devolve for users from that point.
Then we’ll need about ten years for the next generation of hypermedia to surface, which hopefully won’t have Turing-complete scripting on principle. But I’m not sure whether developers are smart enough to avoid repeating the same mistakes again and again…
At least when Flash was common, full-Flash sites were not really as common as JS-only SPAs today, and it was easy to just block embedded plugins by default and only enable when necessary for some particular interactive element. In other words, plugins provided a clear separation between the "document browser" and the "very interactive", but with today's "JS everywhere", that distinction is getting more blurred and difficult to tease apart.
But I don't think this will be the business model of the Web at large. Server costs would be too high. Webassembly blobs with WebGL gives you the sweet spot by offloading the compute cost to the user while stripping them practically all of their freedoms.