The 2021 edition, while a breaking change, will affect only a tiny amount of code. Most crates will be able to put `edition = "2021"` into Cargo.toml without any other modiciations. Only some relatively minor parsing and semantics changes were introduced. It's not nearly as big as the 2018 edition, which brought big changes to the module and macro system.<p>Mostly some quality of life improvements.<p>Also note that the Rust compiler remains backwards compatible and continues to support all previous editions. (well, it's only 2015 and 2018 for now)<p>Lot's of work is put into the compiler, but a lot of it is refinement and plumbing at the moment. Big feature work has slowed down a lot (which is probably a good thing).<p>But as some positive news: GAT (generic associated types, a more restrictive variant of higher kinded types) are apparently nearing completion, which can also unblock some very important improvements for the async world (eg `async fn` in traits).<p>I do still really miss some big features though: async in traits, a more flexible dynamic trait system (multi-trait objects, downcasting), generators and specialization.