If you've poked around in AltanaViewer, you would see that there are a number of unused spells in the "Blue Magic" section that have been there for a good while. A number of these are redundant considering what we have already, but let's take a look at a few of them.
Goblin Rush: Three-hit attack + knockback. Could be a mid-level upgrade from Bludgeon or something.
Final Sting: Bees love to use this when they get low on HP. Possible single-target version of Self-destruct.
Dream Flower: Used by those damn mandragoras while leveling in the jungles and during a part of Apollyon. Upgraded Sheep Song probably, not that it would need one.
TP Drainkiss: Like our MP Drainkiss, this comes from leeches. This one could potentially revolutionize how the job is played. However, don't expect this one to be cheap MP-wise, and it wouldn't surprise me if it weren't available until the 60s or 70s.
Aerial Wheel: Ranged stun move used by orcs. We get melee and magic-based stuns, so why not a ranged one too.?
Pandemic Nip: Used by the gnats in the past areas. Single-target damage plus transfers enfeebles to its target. This could be an incredible solo spell, especially against imps with that damn amnesia.
Airy Shield: A move used by those of the ahriman family. Makes caster immune to ranged attacks. For us, it would probably reduce damage by a decent amount, but not all the way to zero.
Magic Barrier: Another ahriman move. BLU version of Rampart would be my guess.
Bubble Armor: Sahagin move that applies shell. No telling what tier of shell that would be in comparison to the white magic spells.
Shell Guard: Defense boost move used by Quadavs. Upgrade to Cocoon, perhaps?
Everyone's Grudge: Staple Tonberry move featured in several of the past FF games. Since the damage from the attack is based on a person's tonberry hate, it wouldn't surprise me if this functioned similar to the Paladin WS Atonement, where enmity played a part in damage. With all these defensive spells, this could work as an interesting BLU tanking spell.
Mortal Ray: Doom? Not no way, not no how!
Now let's look at some possible job traits.
Demon Killer: Would mean not having to drop 400k+ on a sword just for killing imps (yes I know that price tag can't be helped).
Assassin: This would do wonders for BLU/THF, but it would be worthless on any other sub.
Triple Attack: HAHAHAHAHAHAHAHA! No. The refresh from AF2 body or Morrigan's robe would make this god-like for TP. Homam Corazza grants it to jobs that would not have this ability otherwise. However this trait would be viable for someone who's on a long waiting list in their limbus group and may not be seeing a homam body anytime soon, or someone that may not have sea yet.
Fast Cast: OK now this one sounds a bit more realistic than the last two. I know of a few blue mages who have been wanting this one for a good while.
Here's hoping that these don't all suck, but given SE's track record I'm not holding my breath.