Microsoft is quickly writing more and more Rust code these days. They rolled out Rust kernel components even before Linux, and their efforts actually include rewrites rather than making the API available to developers.

There's decades of code in Windows, but the successful conversion for DirectWrite font parsing is probably a sign of things to come. MS seems to even be porting some COM modules to Rust, which would be the last thing I would start to port (so many pointer pointers!).