> The other big one is futures. There’s still no futures executor in std. Async crates have to decide if they want to tie themselves to a single executor (like Tokio) or be compatible. There is no async stream api in std. No async file api. And so on. It’s a compatibility nightmare.

We need useful traits to abstract over async runtimes. But there are a lot of design points for runtimes so this can't ever go into std. There is embassy, for embedded systems. There is monio and glommio built around io-uring. Then there is smol intended to be simple and lightweight. And then there is the kitchensink of tokio.

Clearly embassy is the one we want in the standard library. /s (It is the only one I personally would have a use for. But no, I don't think any of them belong in std. Traits to abstract over them? Yes, absolutely.)

But even your other example of strings: there are many design points for strings too, that might be better fits for specific use cases: string builder (with a capacity, what String in rust is), copy on write, small string optimisation (like compact_str), even interned strings. So your example of a vocabulary type is somewhat flawed, a better example would be Option or Result. Even anyhow and thiserror build on top of those vocabulary types.