>By creating a standard, and allowing multiple implementations, someone creating a new OS or a new CPU architecture can create their own implementation of the language without having to wait for anyone else to deign to create the port.

Why does that require multiple implementations? There's nothing stopping said party from adding support for their OS/arch to rustc directly today. There are multiple examples of this already: fuchsia, Sony PSP, Nintendo Switch, etc [1]. Now if you want support in rustc itself out-of-the-box this does require LLVM support your target as well. But even then, again nothing stopping you from adding LLVM support too. The avr-rust project for instance maintained an LLVM/rustc fork for a while before those patches were upstreamed.

[1] See the wide variety of targets with varying support today: https://doc.rust-lang.org/nightly/rustc/platform-support.htm...