If Green Mage is a thing, its basically sage level of 'free real estate' for the devs. After all what was Green Mage in prior games? A debuffer and buffer specialist. It wielded hammers.
Silences, Blinds, Elemental Damage Resist Buffs, Protect, Shell, Leap (raise move speed), Tranq (raise accuracy), spellbound (extends duration of debuffs and buffs).

I feel if it did become a thing it gets rolled into geomancy or is made into its own thing that revolves around something druidic like plants.