- Cranelift applies less optimizations in exchange for faster compilation times, because it was developed to compile WASM (wasmtime), but turns out that is good enough for Rust debug builds.
- Cranelift does not support the wide range of platforms (AFAIK just X86_64 and some ARM targets)
It's notable that the projects you mentioned mostly don't need to deal with adversarial user input, while the projects I mentioned do. That's one area that Rust shines in.
Same for the Metal shading language. C++ adds exactly nothing useful to a shading language over a C dialect that's extended with vector and matrix math types (at least they didn't pick ObjC or Swift though).
...that's just because of the traditional-game-dev Stockholm syndrome towards C++ (but not too much C++ please!).
> Khronos future for Vulkan
As far as I'm aware Khronos is not planning to move the Vulkan API to C++ - and the 'modern C++' sample code which adds a C++ RAII wrapper on top of the Vulkan C API does more harm than good (especially since lifetime management for Vulkan object is a bit more involved than just adding a class wrapper with a destructor).
