Looks like there is a lot of work involved to have anything done, remind me the issues that the Chrome team said 2 weeks ago.
And for what it's worth, for almost all langauges C <-> X interoperability is a lot cleaner than C++ <-> X. Since almost all languages (including rust) "speak C", both in terms of compiler support and and being able to map every important C concept to a concept in their language. The same isn't true with C++.
One thing to worry about with adding any language (including rust) to the kernel, is that the next good looking language will probably interoperate well with C and not interoperate well with Rust. So there is a much higher cost the second time you try to add a language.
This is something that Rust is acutely aware of. There have been many discussions about the idea of a higher-level "safe ABI", such that languages with notions like counted strings or bounded buffers could interoperate with each other without having to go by way of an unsafe C interface.
I'd say the biggest questions for Linux that may be blocking here relate to LLVM not being available on nearly as many platforms as GCC (many of which will likely never be supported cause they're legacy systems that are only supported in the sense that they aren't purposefully broken) which limits it's use in any core-ish kernel systems.
It's very Chrome and C++ specific, but the problems will likely be similar in practice.