Except the only thing ever mentioned about BLU was in a Live Letter and an Interview that I can't find anymore cause of BLU actually releasing, i'd appreciate it if anyone has it:
Live Letter: http://forum.square-enix.com/ffxiv/threads/191993
Quote:
-A: I think that blue mage is an interesting job because you can learn spells from enemies, but honestly I don't think that it really fits MMORPG party settings. If anything, I think it would work solo and it would be really fun to implement it as a job where you go around and learn abilities from every monster, so I'd definitely like to try and do this, but I'm concerned when it comes to playing in a party players would put up barriers if you haven't learned certain abilities. Additionally, in the event you are able to use abilities forever once you learn them, the difficulty of learning abilities would be high, and we wouldn't be able to balance the system so it wouldn't revolve around procuring your abilities instead of equipment. This wouldn't be practical enough to fit in an MMORPG party setting and conversely if you are swapping in only certain abilities you've learned, the true image of a blue mage would diminish, so this is something that I am concerned with.
At the time there were no plans for it but he had an idea of what he'd like it to be. The reason the community didn't make such a backlash like the official announcement was because they figured over time he'd find a way to implement it into the game in a way we'll enjoy or at the very least use it as a lens like the other Jobs. The second it was announced to be exactly that at an official level did we get the backlash we got now because he had 4 years to think it over and to our dismay the concerns of many were justified. Never did we get some kind of acknowledgement about the concerns and even now we don't get it. Hell Eureka suffers this too and it took Pagos as a failure to get an idea of what the community wanted even though the Feedback from Anemos alone should have given them an idea of what the community would find fun but it took Pagos and multiple nerfs to get the idea across.