> someone would have to pay a team of engineers to rewrite everything

A partial effort has already been made a while back: https://github.com/tianocore/edk2-staging/tree/edkii-rust

However, this uses uefi-rs, which is incompatible with TianoCore's BSD+Patent licensing, and therefore cannot be used as reference material, as the wiki page states: https://github.com/tianocore/tianocore.github.io/wiki/Tasks-...

More recent efforts have also been mentioned in the mailing list: https://edk2.groups.io/g/devel/search?p=recentpostdate%2Fsti... Rust also has a basic standard library implementation now: https://github.com/rust-lang/rust/pull/105861

Some of the challenges in adding Rust to EDKII are described in https://cfp.osfc.io/osfc2020/talk/SLFJTN/. There is some more recent work in this space described in https://microsoft.github.io/mu/WhatAndWhy/rust/, too.