I'm not sure if I see Morpher being a thing since they didn't even return the job in FFTA2. Regardless, the jobs in FF14 are kept in a very streamline fashion so that there's no variability in your performance in that job. This is why Blue Mage is limited based on the way it's implemented. They don't want BLU to be queuing for duties despite missing spells or using gimmicky spells that are either useless or flat out OP, at least not for regular progress. This isn't FF11. I could see it maybe as a limited job, but I'd rather they continue developing BLU and let it eventually evolve into a job that actually can perform in a streamline fashion and be used in normal content one day.
Some jobs that I do think are either more likely or could be good editions:
Geomancer - Just because they might use earth/wind/water doesn't mean their application has to be the same as Conjurer's. Lots of jobs have fire attacks, for example, and that doesn't make them Black Mage clones.
Apothecary - Virtually the same as "chemist" that gets talked about a lot. I strongly prefer the name "Apothecary" though because there's less direct overlap with the Alchemist crafting job.
Minstrel/Flautist - This is an odd one since Bard exists, but Bard's more 80% archery, 20% music. It could be cool to have an exclusive musician playing healing songs.
Dreamweaver - Since the BLU has introduced the Whalaquee people of the New World, perhaps we could have someone traveling to Eorzea from there teaching people the art of healing through dreams? Random thought, but I would die for the aesthetic.
Drain Healer - I'd say "Necromancer" falls into this category, which others have also talked about. I'm not really sure how much I like that name though, since that is a fairly traditional class in RPGs that is essentially the opposite of a healer. Something along the lines of that or a Vampire (as seen by Bravely Default) could be feasible.