People over-index on "formal" here, the Rust reference and Ferrocene (which will end up being adopted as the official spec) is just as "formal" as the C++ specification.
There are other compilers in development, and they're able to coordinate with these documents. There is of course always more work to do, but it's really not as far away as some people believe.
International standards have nothing to do with formality in the computer science sense.
US corporations also have massive influence on the C and C++ specifications, just look at the brouhaha around Bloomberg and contracts for C++, for example.
And the Rust Foundation does not author the specification, the Rust Project does. So in many ways, companies on the Foundation board have less direct influence than the companies who send their employees as representative to WG21 or similar.
My use of formal was from: “The standard is not intended to teach how to use C++. Rather, it is an international treaty – a formal, legal, and sometimes mind-numbingly detailed technical document intended primarily for people writing C++ compilers and standard library implementations.”
There are other compilers in development, and they're able to coordinate with these documents. There is of course always more work to do, but it's really not as far away as some people believe.