I personally feel like blizz should break up classes and allow characters to pick specs from a grid of related specs, for example you could pick holy priest, ret paladin and prot paladin because they all use light.
This way they could add in new specs without the need to dedicate an entire class to it. Necromancer would be great as a single spec, but would be very thin as a whole class being added into a game already saturated with edgy casters. likewise dark ranger honestly doesnt have enough lore behind it to warrant a full class but would be great as an optional spec for death knights or hunters.
This system could also enable many more specs that exist in the game but dont justify a full class, like shadow hunter, priestess of the moon, zealot, cultist etc. things that should realistically never get their own class but could be added as a spec to related specs.