They did cite Rust's safety as a motivating factor for the port. That doesn't imply trying to achieve that simultaneously with the language change — which is good, because that would be insane. (Or, if you prefer, even more insane.)

You cannot faithfully port a codebase to a new language while also radically re-architecting it. You have to choose.

They want the safety benefits of Rust going forward; i.e., after it's finished, when they then write new code in Rust.