I didn't intend to give the impression that Apple was definitely going to use jxl-rs. You're correct; there's been total radio silence from the Safari/WebKit team regarding anything related to Rust.
But it makes so much sense for Apple, Mozilla, and Google to support jxl-rs. Of course, that doesn't mean it's going to happen.
Keeping quiet and then adding jxl-rs to a dot release like Safari 27.4 or something is also a very Apple thing to do.