They do belong in Rust, but they don't belong in a minor version release. There was Rust 2015, and then there was Rust 2018, we can put them in Rust 2021 (assum

They do belong in Rust, but they don't belong in a minor version release. There was Rust 2015, and then there was Rust 2018, we can put them in Rust 2021 (assuming 3 year cycle). Don't put major new forward compatibility breaking features in a minor release.