I personally want the next healer job to be Necromancer, they already kinda teased it with the second boss in Heroes Gauntlet, and Yoshi p is a big fan of Tactics ogre which heavily features Necromancers.
Also in TO necromancy has a few of healing type spells, albeit for undead units only, but you could just do some funky stuff with the lore to pretend all the necro's party members are zombies xD.

It would also give an excuse to make a healer with a more fun and complex dps rotation too, similar to SMN, you could have a summon undead unit spell, and attacks commands similar to egi assault.