Someone has to write the platform-specific backend. A language standard doesn't help you if nothing implements it for your new platform.

Which Rust still does not have. If serious projects like Git and Linux are adopting Rust, the Rust team might want to consider writing a spec.

A specification is not a standard. It's a good first start, but what makes a standard more valuable is that it requires more than one entity to approve a change to it. This does look like a step in the right direction though.