When you do need wasm, though, then it opens up entire new possibilities, things you really couldn't do before. I like to compare wasm to the video element: not every site should use it, and it won't replace JS or CSS or HTML, but its existence makes things like YouTube and Netflix possible.
The future of code on the web is JS + wasm.
That said: I don't think you need to worry about JS receding for at least another decade, maybe two.
That’ll be the end of frontend as we know it, and everyone will have to learn this new api. The benefits are obvious, we’ll finally have a rendering engine for apps. I suppose document-based html pages can stick around, but the rest of us can move on.
Even I think something like that is long overdue (as the misuse of HTML and DOM as the most horrible GUI framework for application development ever invented should stop immediately) I somehow don't like the outlook of MS Blazor becoming a thing. I hope everybody knows what that would mean: "Windows" (APIs) in the browser…
QML on the other hands side looks good (at least from the outside). But it's nowhere close to significant usage, so no hope for that, frankly.
WebAssembly made us regress 10 years, and we lost the great GUI based tooling for Web page creation and 3D games that are actually hardware accelerated without browsers doing blacklists.