There are many computing platforms that rust devs simply cannot be bothered to support (for just one example, Cygwin). The Python devs, by contrast, have actually put in a lot of work over the years to support a plethora of operating systems and architectures.
Requiring Rust as a CPython dependency would be to abandon all their users stuck in obscure environments.
> The Python devs, by contrast, have actually put in a lot of work over the years to support a plethora of operating system
This pre-pep is proposed by core Python devs. The discussion includes comparing the supported targets of both Python and Rust, the people who are left worse off are devs external to both groups, who've made Python work on unsupported targets (e.g. Gentoo, who are represented in the thread).
The proposal is a long way off from a complete rewrite. It would be many years before end users were even compelled to use a Rust-required CPython to have a supported version.
Requiring Rust as a CPython dependency would be to abandon all their users stuck in obscure environments.
This pre-pep is proposed by core Python devs. The discussion includes comparing the supported targets of both Python and Rust, the people who are left worse off are devs external to both groups, who've made Python work on unsupported targets (e.g. Gentoo, who are represented in the thread).