"I assume that such shields would be only Magic OR Physical armor, not both combined, and that the armor provided by shields remains at current "meh" levels.

Even so, that means having a shield is free immunity from CC attacks from whatever type of damage the shield blocks."

It wouldn't because the way CC works penetrating armor means the CC hits. As well the CPU could just damage through it.

As well Shields should be both... You are sacrificing a weapon and a lot of damage.