Be they taught in Mirage, or Empyrea, or even by Cyrio in the Arcanum, I think these would be nice additions:
Solar & Lunar Shields. Enchanced versions of existing shields (-80% dual, -90% solo, -60% triple). A shield of some kind (single, with , as the new Stone Wall, something along those lines). The Immortal's Triplets (the 'Wall's). Maybe have Kite Shield for only. Bronze Armour. More for than say , just to keep with the school themes. Pierce Resist/Immune (maybe like a 60% Tower Shield with 10% pierce resist being hit by different people. No pierce, 60% shield. 25% pierce, 45% shield).
I can't think of many more, but since I don't think my has had a shield since Cyclops Lane, it just seems like a mechanic to revitalise, especially with pierce being more and more important.
We already have a +10 sun enchant for shields. A Balance shield should never be added in my opinion. For the same reason there's no Prism. It's already offset by Balance having no school blades, only weaker universal ones, and no ability to wand away charms without wasting blades. It takes away the uniqueness of the school.
I echo SeeThe42's sentiment with the caveat that the "Bolstered Ward" Spell to which you are referring should be trainable from Qyburn Stellargaze and that if Ice got a -70% or 90% shield that would be okay. I don't think that we need to homogenize the classes by giving everyone a new shield if that is part of Ice's specialization.
shield of some kind (single, with 
, as the new Stone Wall, something along those lines).
than say 
, just to keep with the school themes.
