According to the notes here[1], it sounds like companies care enough about bootstrapping Rust that they are doing it via mrustc. Which seems pretty extreme and suggests they care... a lot. (This was surprising to me to find out, at least, the degree to which they care. I understand why bootstrapping is itself an important ideal.)
[1] - https://users.rust-lang.org/t/rust-in-large-organizations-me...