Thank you for your replies. This matches my expectations, but I wanted to confirm.

One thing I still have an open question on is using non-GPL but GPL-compatible libraries. Ignoring Rust, would that be accepted in C? Or do all libraries need to be GPL as well?
On Jan 22, 2023 at 7:04 AM -0700, Po Lu <luangruo@yahoo.com>, wrote:
> Daniel Martín <mardani29@yahoo.es> writes:
>
> > This answer is not exclusive to Rust. I don't see any clear net benefit
> > from using another language along with C (even C++) in Emacs core.
>
> Exactly.
>
> Now, if someone wants to contribute a port to Redox OS, and the port
> code uses Rust, that would be something else.
>
> For example, the NS port uses Objective-C, the Haiku port uses C++, and
> the Android port uses Java.
>
> However, Redox has a C runtime, so I doubt that will be necessary.