We are planning to add that functionality eventually, but it won't be available right away. This is because we developed the new Admin as a drop-in replacement for our old Flash-based Admin, minimizing any changes required in the back-end routines they use to save new settings and load existing ones to view/edit.
At present, the back-end has no way of passing detailed, discrete settings for existing shipping rules back to the front-end Admin where they could be viewed/edited; it only passes the pre-fab summaries exactly as shown in the Existing Shipping Rules menu. Once the new Admin is fully live for everyone, we can start considering new features and functionality that would require more extensive modification to the Admin back-end for managing their settings, such as the ability to edit existing shipping rules.