That would be great. But it's not simple to put in place as you need to load all the order information as it is loaded during the checkout so that the shipping method can process all that again and propose a new price.
That's surely a good idea but not a high priority for us at the moment.
That's something which you could do, if you know PHP, by editing the view of that popup ( file "changeplugin" of the view "order" ) and loading the order info and calling the shipping method event to get the shipping price.