To add on to the siblings one of the major motivating use cases for rust is to interact with another GC, originally the JS runtime GC for the servo browser. An

To add on to the siblings one of the major motivating use cases for rust is to interact with another GC, originally the JS runtime GC for the servo browser. An on-by-default one would interfere with that usecase heavily. What I could see and there have been some half-hearted efforts in this direction is to standardize on a `Trace` trait so that users who want to bring their own GC can do so safely and can allocate std lib objects into the GC heap without concern.