we can talk of this in every sense possible, either vampire or blue mage, you forget one point quite important in all of this...
Yoshida did said in the past that he will bring class that will bring new stuff to the game and group. however, what will bring the blue mage, that like the red mage end to be a jack of all trade jobs. we can expect a red mage will will loose one face of him capacity, because we are into a mmorpg, not a solo game.
what work for a solo game with a jobs that can do everything but master none, can't be done into a mmorpg, why you ask? because it will lead to a jobs either too powerfull, rending other jobs useless (that will lead to a massive nerf later) or a useless jobs in the sense that since it can do everything, any one specialized will be more interesting. meaning, he will deal decent damage, but will be far less interesting than another dps, he will be able to heal, but not enough in end game content, he will be able to tank but be unable to tank end game content.
for make simple, if they bring this sort of jobs, they need to specialized them, we can see already how semi hybridation lead to weird stuff, like the machinist and bard, that have a few capacity of support, but with reduced dps. in content that anyone can do, like midas normal, dungeon or void ark, them dps are lacking seriously and even with a good stuff will simply be less powerfull than other dps. them utility shine in high end content, where them song/drone can be very important for high end encounter. but we talk of what? 3-5% of the content of the game.... that too little...
i'm sad for the bard and machinist that have to deal with this, i will have prefer yoshida to bring a true full support jobs than saying, people will not love to play it... even if people don't love to play it, some will have enjoy this sort of gameplay. but i digress.... the blue mage/vampire are not tailored for a mmorpg in the form we know it (from solo game) and don't give me FF11 as exemple since this game was well know for have a disastrous balance.
for now, we must maybe look in the direction of jobs that can be bring to the game while still not feel half assed.... and seriously, between what you can imagine and what they can do.... you have a world. with if we can put paris into a bottle (it's french proverb) but it resume well what i see there into this thread. a If we do the bluemage like this or if they try to do this.... only them know what they can bring or not to the game. but for me right now, the blue mage even if it's asked, need to wait a long way before being bring to the game.
i will finish with this, they have said that they will never ever redo 3 jobs at the same time, we can expect 1 or 2 jobs from the next expansion... and i doubt blue mage is them... and even after this with where lead the story, i doubt the blue mage will make it even in the next expasion, exept if they create a new type of "blue magic" that will probably not please everyone... and i can already see a lot of displeased player if they bring the red mage like it was teased last years, since it will not be the red mage of the solo game...
ps: before i forget, add content cost them time, energy and money... create a jobs that will recquire a whole new system for learn it skill randomly will be a major pain in the ass and most player will refuse to play it... since you can end to not learn a skill for hours if you must go hunt a type of monster for X skill.