Every weapon and armorpiece has one or more enchantments except, the shield? The enchantments can even have similar properties to that of the sword, bow, or armor. You should add:
-Firebrand: sets mob on fire when the shield successfully blocks an attack
-Shockwave: increases knockback on mobs when making a successful block
-Barrage: the rarest of the shield enchantments, deals sweeping damage to a group of mobs in a successful block, but at a random chance like Thorns
-Fortress: could expand the radius of the shield's protection by one extra block, or it could give protection to another player one block adjacent to the wielder, whether or not that player had a shield that was plain or enchanted.