I know Blue Mage is been quite a controversial subject, but I personally feel pretty satisfied on how it works, so I won't be mentioning whether would be good or not it becoming a "mainstream" job.
The big issue (for me) though, is the longevity of the job's actual repeatable content.
Masked Carnivale and the Blue Mage "PF" Log are flawed, because for - endgame content category - they have pretty niche goals, practical use and rewards. Deep Dungeons, however, would be the perfect candidate for a repeatable activity for the soloing Blue Mage.
1) It's not a predictable solo activity like Masked Carnivale, you need to be constantly thinking and adapting and figuring out what is the best composition of spells to bring, given that they probably wouldn't be able to be swapped on the go.
2) There are a ton of random rewards to be obtained with the pomanders of Intuition. That by itself is already a really cool reason to push through the floors. Even right now, some of the relic weapon steps are tied to deep dungeons, I would totally be getting those there, even at a lower rate, with a Blue Mage rather than running those endless Delubrums.
3) Blue Mages could have their own scoreboard and soloing achievement, so it wouldn't invalidate the other job's soloing attempts; in fact, they would probably still be much harder, given the limited utility.
Beyond that, I really don't think that group content is bad for the job - it's really fun, for example, to push through the achievement to get the mount - but I'd love if they kept true to the inital idea and really made more Blue Mage's content that is tailored for the solo player, and content with longer shelf life.