It's not exactly for convenience. The Rust GC support isn't intended to be used in general situations. It's for integrating with languages/applications that have a GC, like spidermonkey or V8.
https://github.com/manishearth/rust-gc actually lets you cleanly mix GC and non-GC heap objects (even put pointers to GC heap objects on the malloc heap and vice versa). So does Servo's current bindings to spidermonkey.
https://github.com/manishearth/rust-gc actually lets you cleanly mix GC and non-GC heap objects (even put pointers to GC heap objects on the malloc heap and vice versa). So does Servo's current bindings to spidermonkey.