I think none of your points are really set in stone.

* The kernel already contains some C++ which (if you ask C programmers) is not C. And many C programmers are more likely to accept Rust than having to deal with C++.

* AFAIK there is not gcc front-end for Rust yet but LLVM tools can compile the kernel, too. When Rust stabilizes gcc support may come, too.

* The barrier for entry could be lowered by using Rust for Rust programmers if it is employed in some specific modules. The resulting code could be more clear. Not everything in the kernel is pointer pointing and bit shuffling.

* The number of architectures that Rust supports are growing daily.