Let's say such a change happens and at that time there's a bit of time pressure and the capacity on the rust maintainers is thing for whatever reasons. Will they still happily swallow that change or will they start to discuss if it's really necessary to do that change? And suddenly, the C-maintainer has a political discussion on top of the technical issue they wanted to solve.

This situation could occur even if the code using the API was written in C.

If an API change breaks other downstream kernel code, and that code can't be fixed in time then they have a conversation about pushing the changes to the next build.

In the end, Linus has already chosen to accept the extra development overhead in using Rust. I think this situation was more about a maintainer, who happens to disagree with the Rust inclusion, using their position to create unnecessary friction for other maintainers.