I don't feel like this has a point anymore. Shield spec is pretty bad to be honest in PvP, because your shield won't absorb more than half the attacks thrown at it. The biggest damage attacks go through your armor as well... it's AWESOME.
This is the point where they need to take at least a little learning from WAR. They finished running that game into the ground, so it's no big deal if they do this now anyway.
Shields should block EVERYTHING. That's right. If a squirrel runs up to me, I need to have a 50% chance of punting him back with high powered deflector shielding. It doesn't necessarily need to absorb ALL the damage flat out, but for the sake of the class, this spec needs to soak up damage in PvP because it CANNOT deal it like a Tankasin or even a Jugg.
Pure tanks are useless in pvp, anyone who knows the pvp mechanics should know this. Shield only protects against white damage, which means anyone doing MOSTLY elemental damage( BH DPS), force damage( Sorceror and Assasin) , and tech(operative) will completely go passed your shield and ignore your armor. the only tank that is viable in pvp is a hybrid,, built to deal damage and survive fights.
As a vanguard tank hybrid, you need to focus on buffing your elemental dmg while still be able to use the tank stance.