I've beaten the masked carnivale, gotten every spell and done all the achievements, so I feel like I've done everything there is to do on BLU right now and I'm ready to look to the future.
Future spells
Having completed the spell list there are a few moves it feels like BLU is lacking.
-Raise/reraise.
Basically the primary reason that BLUs don't do all BLU runs for primals and such to learn their spells is if you die, you don't learn the spell. Since BLUs have no way to revive themselves or each other this means if you die and everyone else learns the spell then tough luck. If they could revive themselves it would go a long way to seeing all BLU parties.
-Healing and tanking.
In the same vein as above, BLU lacks the tools to specialise as a healer or a tank, making it hard for all BLU parties to work.
Mighty guard is ok as a tank stance although it cripples any AoE potential since it requires off guard to negate the damage penalty to any significant degree. Making ice spikes, the look and veil of the whorl ignore the mighty guard penalty would fix this issue.
Another tanking issue with BLU is that it has no provoke skill, if there are mechanics with a tank swap the only way to handle it with all BLUs is to lucid dreaming away your enmity and hope someone else is close enough behind you to take it which is not ideal.
For mitigation, diamondback is great, but due to the high mp cost and locking the BLU in place it doesn't make for a sustainable mitigation tool. Same goes for white wind, the mp cost is high and if the BLU gets too low on hp it becomes less effective thus requiring even more mp, BLU needs more healing and mitigation tools, even just a cheap self heal like pollen in ffxi and a minor mitigation buff like cocoon would really bring BLU up to code.
Useless spells
Now, I've got nothing against the carnivale having little gimmicks in the fights that make you use specific spells to beat them. What I'm not ok with is those spells having no purpose outside of that one gimmick.
You want to make mobs heavy me so I have to use loom? Fine. You want to design loom so it's completely useless to BLU outside of that one specific scenario? Not fine. This could easily have had no cast time and been a BLU version of shukuchi, but no they gave it a cast time to the point where unless you're heavied you're better off just walking. This was a silly design choice and it just clogs the blue magic spell list with spells that could have worked but don't.
I'd like to see this system reworked so these spells all have a purpose outside of the carnivale. As mentioned above, remove the cast time from loom and it becomes useful. The primal skills are another one where the moves are just clones of each other with different elements which has no meaning outside the carnivale, these could have different effects or uses, like how glass dance and veil of the whorl share a recast but veil is better for tanking while glass dance is better for dpsing. The same can be said for a lot of BLUs dps spells like the breath spells. It just feels like a waste to make these spells exclusively useful in the carnivale when they could be bringing something more to BLUs kit.
Spell learning cap
I understand that these spells are supposed to be rare and keep BLUs running primals into the foreseeable future. But the drop rate on these spells is soooo annoying!! What I thought would be a good idea would be to let us buy empty whalaqee totems and as we fight the primal it fills with aether and once its full we can use the totem to learn the spell, so after say 99 runs of titan not getting the spell you could use the totem to learn it, just putting an upper limit on how many times we have to do the fight similar to mount farms would really alleviate some frustration. Even if you'll never hit that upper limit, just knowing that it's there will make the grind so much more bearable.
That's all I have off the top of my head. What things would you like to see on BLU going forward? (We are assuming it's going to remain a limited job, please no "make it a full job" posts, I want it to but I don't see it happening based on the interviews and live letters).