I'm not terribly familiar with how Blue Mage worked in other FF games but my mind is swimming with possibilities.
My hope/theory is that this job will have a unique layer of customization to it, allowing players to mix and match various abilities freely. Certain combinations can optimize it for different roles, so it could be possible to play BLU as a Tank, Healer, or DPS. So maybe it will be similar to the Logograms system from Eureka Pyros (I haven't made it to Pyros yet so I'm just going off what little information I've gleaned)?
Of course if this is the case then people will undoubtedly find the "best" skill set to use rendering customization pointless, not to mention balancing the job would be absolute hell. But maybe that's why they're releasing it as a "Beta test" of sorts.