Let's be honest with the BLU. In any game that had them, while they may have had a ton of spells total, there were really only a handful that were all that good. Stuff like mighty guard or white wind and maybe a decent nuke or attack, but most of it became redundant by the time you had them all. So even if you had any old class, then picked 5 of the more iconic BLU magic spells as the Job abilities that you learned via the Job quests, you'd still be able to hit most of the high points.
However, a way that BLU could work in FFXIV would be to make the BLU a tank job. One of their more important abilities would be "Learn", which would reduce the damage of the next incoming special attack by 20-30% or whatever. When abilities are learned, they will grant the tank one charge of that ability and then the Learn ability will change to "Unleash". This will allow them to hit the enemy right back with the ability that was just absorbed. Wouldn't it be pretty cool to absorb titan's table flip and then turn around and cast it right back at him? Learn/Unleash would be the level 30 job ability, and the remaining abilities would be iconic BLU magic spells that you learn permanently via quest.
