Rust is noisy in other parts, for other reasons (trying to explain to compiler how to write super fast and data-race free code). But visibility qualifiers are not a problem.
`extern` is only for importing crates, which is like 10 lines at in whole package/crate. Irrelevant.
Ultimately in the end, for this example it really seems like the same amount of work. You add one word, I run one command.
You are incorrect on multiple fronts - 1) there is not even an active proposal to this effect, its just an idea that was passed around and not even really discussed, 2) the idea did not involve making rustc depend on cargo at all. It would be shocking to me for the Rust community to ever accept a proposal which required rustc to depend on cargo.
In general, please try to avoid contributing to the spread of misinformation by not stating as facts things you are not very confident are true.