It is way too early to standardize any such thing now. There are, give or take, 5 promising UI toolkits, and a dozen others that are best thought of as experimental and may contain interesting ideas. There's a very wide diversity in approaches, and much of that diversity is not accidental but can be traced to different requirements. If you need to deploy an app both on the web and natively, then that pushes you toward adopting at least some web technologies. If you're working on games or game tooling, then the tradeoffs of immediate mode GUI are much more appealing. Another major axis is how much to rely on platform capabilities for stuff like text layout vs rolling your own.

We need to do a lot more exploration of the design space. I believe there is potential to build really compelling UI in Rust. It's entirely possible we end up with fairly different approaches for different use cases, hopefully converging on common infrastructure for things like accessibility.

But if we standardize anything we have now, it risks "the standard library is where modules go to die."