And what about allocations and threads?
let x = vec![1, 2, 3]; let a = &mut x[0]; let b = &mut x[1]; swap(a, b);
Because Rust doesn't really know the difference between the whole Vec an element within the vec. Therefore it treats any mutation as one that could potentially invalidate anything with the same lifetime and doesn't compile. So I believe the plane model to be strictly better because it allows for this and still prevents the real scary thing:
let x = vec![1, 2]; let a = &mut x[0]; x.push(3); a = a + 1;