Historically, the answer to that was "yeah totally." But folks have put a lot of work into getting clang to build the kernel, and IIRC Google has been building their Android kernels with clang for a few years now.

~~It's not~~ (see below) It wasn't supported directly by upstream, and in fact historically was pretty much the opposite: the intention was to not care about portability between compilers at all.

It's one thing to say developers have to add a new compiler front end for some drivers if they want to compile them; and, that some developers will just have to add it regardless.

It is wholly another to say that they need adopt a whole different code-generation regime. It adds risk, and adds to what they need to understand to know what they are building. A pro needs to understand where problems come from, and be equipped to dig down to them.

So, OK for hobbyists, but a burden for pros. It is the difference between "neat project, might succeed" and "mature". Rust stands a good chance of becoming mature in a few years, more than can be said about almost everything else.