I thought about this before as well. I didn't like the idea of shields stacking as a defense. What could someone do if they stacked emerald shields? They are immortal, and in my mind most shields couldn't attack, so they really couldn't be killed. My thought was if you animated a shield, it would protect your creatures. So say if you animated a dimensional shield, your creatures would gain quintessence for 3 turns. Or if you animated a dissipation shield, if something would damage a creature, it would damage quanta instead.
That being said, I had no ideas when it came to shields such as the gravity shield. But I do like the concept of an animate shield card, just not sure what it should be like.