What would Rust look like if it was re-designed today?

What if we could re-design Rust from scratch, with the hindsight that we now have after 10 years. What would be done differently?

This does not include changes that can be potentially implemented in the future, in an edition boundary for example. Such as fixing the Range type to be Copy and implement IntoIterator. There is an RFC for that (https://rust-lang.github.io/rfcs/3550-new-range.html)

Rather, I want to spark a discussion about changes that would be good to have in the language but unfortunately will never be implemented (as they would require Rust 2.0 which is never going to happen).

Some thoughts from me:

• Index trait should return an Option instead of panic. .unwrap() should be explicit. We don't have this because at the beginning there was no generic associated types.
• Many methods in the standard library have incosistent API or bad names. For example, map_or and map_or_else methods on Option/Result as infamous examples. format! uses the long name while dbg! is shortened. On char the methods is_* take char by value, but the is_ascii_* take by immutable reference.
• Mutex poisoning should not be the default
• Use funct[T]() for generics instead of turbofish funct::<T>()
• #[must_use] should have been opt-out instead of opt-in
• type keyword should have a different name. type is a very useful identifier to have. and type itself is a misleading keyword, since it is just an alias.