Salve-Maker as a Chemist job separate from Alchemist would be a fun one. Would love to have Feel No Pain as a ability. Make it an Ult skill that delays damage for 5 to 10 seconds before the you take all damage in full. Would be an interesting gimmick. And besides class specific healing potions you could throw out buffs.

Or have a Necromancer or similar class do the bulk of it's healing simply by attacking the enemy.

It would be nice to have 2 healers that focus more on healing and another Healer that prioritizes DPS more alongside the WHM.

It's not impossible to introduce a 4th spec and balance the 4. Tanks for reference are more balanced in DPS across the board more then ever.

However I think that as level cap increases we are more likely to see Blue Mage and White Wind serve as a 4th healer before getting a new one.