You mean like this thread? If anything, the fact that 1) there are so many ways that it can be implemented, 2) everyone seems to have their own idea of how Blue Mage should work in XIV and 3) most of those ideas (including the one that I linked) won't work in this level of the game show how little we--the players--know of the game.
However, in making a Blue Mage concept back during Heavensward and then seeing the job in the game now, the only real takeaway seems to be that those who clamored for the job like it was in XI honestly got what they wished for: a job where you could go out and learn spells just like they could in XI, which resulted in a job appearing to be just as impractical as any other concept pulled right out of one game and slapped into another seemingly without any realistic adjustments that would make it suitable for all aspects of the game. Such adjustments would include an alternate resource system (a "job gauge"), changing or removing of all spells that work around percentage of health or have status effects other than stun or sleep that boss-type enemies would be immune to, and creating a somewhat-forced rotation that would mean removing the need to hunt specific mobs for spells and forcing the learning of spells into level growth and questlines. Yes, a "gating" system could be done where a Blue Mage couldn't enter certain dungeons, raids or trials because they don't have a specific spell or spell set except 1) this system screws over players with worse luck, 2) devs would have to painstakingly set those requirements for each and every single bit of instanced content and 3) players would of course whine and complain about specific requirement settings; all of this leads to far too much micromanagement work required of devs that could be busy doing a multitude of other things. In short, making Blue Mage a regular job requires eliminating everything from Blue Mage that regular jobs neither have nor do.
That being said, I'm still not convinced we have enough information on Limited Jobs to really know if they're a bad thing or not. All we have is Blue Mage, one of the most highly demanded jobs for years left prone to some really bad explanations from devs as to why it is what it is in XIV. There is potential for it as a way of offering more appeal for open-world content, and maybe Blue Mage would be more popular if it didn't require going into dungeons or trials and truly was a solo gameplay experience. Either way, I'd still withhold my judgment on Limited Jobs until another one comes out and HOPEFULLY it will have a far better excuse stated as to why such a job is declared Limited.