Like a lot of people here have mentioned, a lot of what makes Blue Mage itself and its identity boils down to abilities that in some cases are just blatantly overpowered so they can't really incorporate them. I.E Missile, or low level mobs vs 1000 needles. The only way you'd see them in current content would require them to basically do away with what makes Blue Mage itself.
Another thing they could, and I wish they'd do is introduce more limited jobs, then make limited jobs able to queue with each other. I.E Like Mime, or Puppetmaster. The idea should be expanding Limited Jobs and making them all sort of interact with each other and do raid content so a limited job isn't just you and a handful of other people who are engaging with it. Once that is achieved it not only increases the amount of things to do, it allows for an entirely different community and a lot more job potential for things they want to do, but just can't make work. Hell, if you do that why not even go whole hog with it, add abilities to bosses that Blue Mages can learn from current tier, if you do Puppetmaster enable bosses to drop components they can use to buff their puppets in some regard like plating or weapons. That way you could make it like a sort of "It's designed around the first kill to get your stuff, then after that it kind of quickly becomes simple" because to justify those classes going in there aside from gear and prestige, they should drop things to aid the class, like Blue Mage spells. Add achievements to kill bosses without anyone in your party having used something that would simplify it like a spell from the raid.
I think a lot of the ire directed at Limited Jobs as a concept is they really are only a minigame without any actual endgame to themselves and right now it's exclusively blue mages. Throw in a few more classes, add a limited jobs only queue function once you add more and it can be like its own little community that doesn't feel like an isolated kid they throw toys at every so often to keep them entertained and away from others in the house.