[plopz]

The issue is references, if you de-reference in the data function, you can now never change that reference because Vue's reactivity won't see the change.

    let external = {foo: {bar: 'something'};
    new Vue({
      data: function() {
        return {
          ref: external.foo.bar
        };
      }
    })
    external.foo = {bar: 'something else'};