You can't cut down a language without breaking changes. And there fairly often are internal changes to simplify the compiler and the tooling. Just in the latest release, annotation internals were finally fully unified between rustc, cargo, clippy and other tools. This was a fairly considerable effort in deduplicating code. Borrow checker is being rewritten to move to tree borrows, trait resolution is being refactored for a variety of reasons. Code is being simplified where possible, but this doesn't mean Rust doesn't have areas to improve in, especially if there is a goal of replacing Ada/SPARK