Rust is going to be used often, but we are open to other choices when they make sense.

Since most unsafe code is C or C++, Rust usually makes the most sense for rewriting one component at a time. It integrates with C and C++ very cleanly because it has good FFI and no runtime.

If we were rewriting more projects from scratch and integration with existing C and C++ code was not important, we might use other languages more often. I don't expect we'll attempt to rewrite many pieces of software from scratch.

Source: I run the memory safety initiative at ISRG.