Why not make mage armor baseline and nerf it a little so that is not overpowered since it would be baseline. Blizzard would know how to nerf it hopefully. I know each armor is based for each spec( Arcane, Fire, Frost) and so it makes the most sense to have the Arcane armor be the one baseline.
Mages would still have to choose between 2 armors ( fire, frost ) depending on the situation and what we want to do but it wouldn't make the third option just another spell on the spellbook that its never used. I think this would help refine the mage class in the long term while still allowing the choice between armors. Thoughts ?