There are a couple of proof-of-concept libraries adding a `Gc<T> where T: Traceable`, so it is doable. You can't change the existing Rc, because it's a concrete type. Making it use a tracing GC internally would require a lot of compiler magic.

However, I don't think a GC will catch on in Rust in its current form. Rust's userbase likes it as a no-GC language. Plus a 3rd party library GC wrapper type can't save you from having to learn ownership and lifetimes used by literally everything else. Once you invest time to learn the "zero-cost" references, a runtime Gc is less appealing, and won't be as ergonomic than the built-in references.

Swift, OCaml, and Mojo are trying to add some subset of Rust-like ownership and borrowing, but in a simpler form.