Give necromancers more “powerful” types of undead, like for example vyrkur, liches, skeletal mages, etc.
As for spell breakers/battle mages, they can create a story where they use arcane rune magic stored in their sheilds for different effects.
There is this thing called a magic chart. WoW has several different magical types with their own rules on what they can more easily do or struggle to do. This isn’t harry potter.
Sword board dps spec/arcane style tank or healing. (Spell breaker) also another class that could use mail. We lack a mail tank for some strange reason, lack a sword and board dps, and brings a new flavor of class into the game (since mage blades or in pathfinder terms magus seeks battle and want to challenge themselves in combat) of an arcane user that actively find new ways of fighting. This would also bring in a new sheild class (something not brought in since vanilla)
Necromancer: A new type of focused pet gameplay, we lack a class that uses ranged pets. We also could use more frost/unholy type of fighting. One can even focus on the user becoming a lich himself which reflects on necromancer lore. We also did not get a new cloth class in forever.