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.