Hm. One example from the article:

    match map.get_mut(&key) {
    //    --- first mutable borrow occurs here
        Some(value) => value,
        None => {
            map.insert(key, V::default());
            //  ^~~~~~ error[E0499]: cannot borrow `*map` as mutable more than once at a time
            map.get_mut(&key).unwrap()
        }
    }

That's a limitation of the current Rust borrow checker. The problem is that the argument of match is never used again on the None path, which should end the range of the borrow before the None branch starts. But, currently, it doesn't. The range of the borrow is too closely tied to scope.

This is supposed to be fixed with the Polonius borrow checker. It doesn't require a new language, just something that ends the lifetime of a borrow at the last use.

Wasn't this covered yesterday with the article about the Vale language? It seems related.

Regarding cycles, that looks interesting. GhostCell dates from 2021 but got stuck at "alpha quality". The usual approach to cycles in Rust, or at least backlinks, involves Rc, RefCell, and Weak. Forward links are strong, back links are weak.

I've suggested creating OwnerRc, which is like Rc but not cloneable. That's a single owner Rc. If you drop an OwnerRc, it panics if there are any outstanding weak links. This is useful because you no longer have to check when upgrading a Weak - it always works.

So these are fixable language problems without the need for a new language and new terminology.