Because I know everyone loves reading other peoples opinions on how classes that aren't even confirmed to be included should be implemented I thought I would weigh in with my idea for Blue Mage.
With the limited numbers of abilities/spells all classes are restricted to we can't have the cornucopia of abilities we were allowed in XI, which hurts the inherent Blue mage flexibility (which to me is the essence of the class).
My idea to compensate for this is to have the spells/abilities to be 'blank vessels' so to speak. You could assign a learnt enemy ability to the blank ability slot which could later be unlearnt or forgotten (possibly via a complementary ability or just a UI option) so it can be reassigned.
eg:
Level 1: Lancet: 10 Second Duration. 30 second Recast. Chance to acquire first enemy job ability used while Lancet is active.
Level 2: Enemy Ability (Single Target). MP Cost: Varies. Recast: Varies. Unleashes learnt Single Target Ability.
Level 4: Enemy Ability (Conal AOE). MP Cost: Varies. Recast: Varies. Unleashes learnt Conal AOE ability. Combo with Enemy Ability (Single Target): Reduced MP cost.
Level 8: Creature Affinity: Slightly increases Lancet effectiveness.
Level 10: Enemy Ability (Enhancing). Mp Cost: Varies. Recast: Varies. Unleashes learnt enhancing ability.
etc
I may not have explained it properly, and I certainly havent developed the idea beyond my own meandering whims but I feel this would keep the Blue Mage's core characteristics without changing the structure of the Classes/Jobs.
1: Flexibility: Blue mage has access to the same wide range of spells they had before.
2: Restrictions: Blue mage cannot set all AOE abilities and end up OP'd in group situations. Also, individual MP costs and recasts could be adjusted accordingly.
3: Monster Hunting: Blue mage needs to actively hunt abilites, the best ones (eg Elbow drop or similar) would need group participation (and most groups would tell the Blue Mage to gtfo because they would not want to wipe to Elbow Drop just to give the Mage his shiny new spell. Also, if a Blue mage resets or forgets a spell and wants it back, he or she would have to go out to learn it again.
4: Awesome animations: You want to see a blue mage perform the frog's belly flop and the cactuar's thousand needles. Admit it.
Flames/Critiques/Love letters welcomed.