first "&" is a mandatory sigil so you have to write
let &exclusive = { foo: { bar: 'baz' } };
const foo = &exclusive.foo
then as foo is like an implicit read-write reference of &exclusive and reference is recursive in the sense that they are applied on object and all these props it raise a "ref error: one mutable ref allowed". As discused if the draft you can't reference an object that allready holding an explicit reference (a parse since the sigil is mandatory) or an implicit reference (at runtime) for ownership reason.
Cloning (and moving) are protocol to implement on object (since deep clone problematic was discussed). Standard global object as to provide an implementation and user defined object herit from "Object" but have to implement their logic. You can see an example of what it could look like (and test it on live example in my github)