Programming

Indeed.

In some ways, this kind of thing is ideal for Rust. It's at it best when you've a good idea of what your data looks like, and you know where it's coming from and going to, and what you really want is a clean implementation that you know has no mistakes. Reimplementing 'core code' that hasn't changed much in twenty years to get rid of any foolish overflows or use-after-free bugs is perfect for it.

Using Rust for exploratory coding, or when the requirements keep changing? I think you've picked the wrong tool for the job. Invalidate a major assumption and have to rewrite the whole damn thing. And like you say; an important choice for big projects as choosing a tool that a lot of people will be able to use. And Window is very big.

They're smoking crack, anyway. A million lines per dev per month? When I'm doing major refactoring, a couple thousand lines per week in the same language, mostly moving existing stuff into a new home, is a substantial change. Three orders of magnitude more with a major language conversion? Get out of here.