Research that has matured enough for Rust 2.0

Do correct me if Im wrong, but I recall that one principle that was used in the development of Rust was to only use tried and tested research material when choosing what to implement. Given we’re more than 10 years out from Rust’s initial development, I’m curious what research ideas have matured enough to either

1. Be added in future editions/versions of Rust, or
2. Be used in whatever successor language might come that follows much of Rust’s philosophy around development.

This is all basically one massive ask about interesting developments in programming and type theory, since I’d like a few new rabbit holes to fall down.

P.S. whatever successor language does come around, I hope it also cultivates a community that takes ergonomics as seriously as performance, because that, even more than memory safety or other aspects of the language, is why I pay attention to this language and ecosystem.