People always compare it to FFXI version, but this isn't XI version - what worked there, doesn't work here, that's why they didn't want to add it in the first place. But they have this tendency to do everything that players shout for, so we got BLU....not quite as they wanted it, because it can't fit into the role system, without ruining it. I don't think they have any intention of adding more limited jobs, just BLU, because it doesn't fit into the system, so it has its own system. If it could fit in, they would already done that.
It's troublesome to balance one new job, but BLU with its huge pile of skills, would be impossible to balance for normal content, without it being OP or UP, or just weird and gimmicky - what's this person even supposed to do??