Rust has never been successfully used to develop large-scale software of the size of SharePoint, Exchange, or anything of that order of magnitude: gigabytes of compiled code with the main executable being 10s of megabytes in size.

An observation I've made about Rust is that because it eschews OOP, it tends not to "scale" to large development teams for single applications. It's great for CLI tools, small web apps, etc... but after some scale it runs out of steam.

This is exacerbated by its glacial compile times compared to other languages, even C++, let alone C#.

I just can't imagine something the size of SharePoint being developed entirely in Rust!