This is already available in ClassicPress, as far I know.
What do you mean by it? That you added a new feature?
The blue messages are OK IMO, but they need to be filterable (do change them as the developer may like).
Also note that the footer text (go back to X and privacy policy) are part of an action and there might be plugins expecting that to be outside the box. But with the changes I see here, everything is going to be inside the box.
Not sure that is backwards compatible.