I have more 'evidence' supporting my want for a mirror shield in the form of the not so long ago GameSpot+Bill Trinen interview, copypasta from ZD Main Page:
They’ve built an entire upgrade system into the game. So for example, right now you can see that Link has his traditional shield, but he actually will get a lot of diferent shields in the game. He will start off with a very basic one, and then as you fight enemies, you will recover these kind of treasures or artifacts that you can then use as resources to upgrade your items.
Notice how the words a lot are listed. A lot typically means 5 or more. Now, 5 shields in a Zelda game...you're probably thinking, what? or something similar to that. And I agree, 5 shields is a little over the top. But you have to think, we're getting articles and treasures for upgrading stuff, with shields being listed under the general category 'stuff'. A mirror shield isn't too much for upgrading purposes, is it? I'd like to believe not.