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!
Think of an app like SharePoint as "Linux Kernel + Drivers + Userspace tools". There's a few large monolithic executables some tens of megabytes in size for each of the core web apps and services, and then hundreds file format converter plugins, database drivers, etc, etc...
Chromium is similar. It's practically an operating system now, it even has USB drivers! I had to compile Chromium from scratch once, for which I spun up a 120-core cloud VM with 456 GB of memory so that it wouldn't take all day.
With Rust... that would take all week even on that box.
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!