It's a neat idea. Turning jobs that have no chance in hell of being added in the game as side content that's free from job balance. Sounds rather interesting. And coming from the forums who are always yelling about "homogenization" and "loss of identity", you'd think more people would be open to the concept. Then again, it is the forums after all.
Isn't that the crux of the matter? BLU not being like the other jobs. Balance and content design just doesn't take it into account and that gives it access to things and capabilities that no other job has. Which in turn comes at a price of not being able to do every content due to content not being accommodating (PotD/HoH) or barred as to not trivialize further (max level content). If it was able to hit 80 today it will still be banned from certain things like Savage and Ultimate.
SE does relatively well with job adaptation because they've mostly stuck with adapting easier job archetypes. The simple ones like PLD, WHM and BLM are all clear-cut and straightforward. And when things get more complicated like say BRD, where in other FF titles it's a support-leaning job that has almost nothing to do with bows, they have to bend the idea to fit what works with the game with varying results. And this can go pretty bad if you look to SMN, that was a name-in only job until several expansions later. Some jobs are just harder to translate from job concept to playable job. Which makes some potential jobs unlikely to be added. I don't have high hopes of seeing Arithmetician being added any time soon.
Pick another job? I'm sure a lot of SMN lovers from the franchise preferred BLM (or any job) over 'doesn't-actually-summon-anything-until-SB' SMN. Honestly, people who love a job concept centered around their fantasies were likely to be disappointed anyway. Some people wanted BLU to be a mage tank, some wanted a duel-wielding battle mage and others a healer with a mix of monster-related gimmicks. All plausible (excluding the spell acquisition and other important factors).