I think that if SE adds BLU they should have it so that the BLU unlocks slots, that function like the cross class system, every 5 levels from the job quests, ending up with 5 slots at 50. Like the cross class skills, you would be able to set your spells and you would still technically have the same amount of skills as all the other jobs. This would allow for the BLU to still feel like a BLU while still limiting the job to keep game balance.

As for learning the spells a few ideas that come to me would be to either:

1. Have the spells linked to the hunting log in some way or even give BLU a seperate kind of HL that is for learning spells.

2. Have guildleve-esque quests that you can undertake that would reward with a spell.

3. Have a combination of 1 and 2 where you complete a HL entry then you would able to initiate a fight with a boss mob, and when defeated it would reward you with a spell.

Again these are just ideas that utilize the current systems in the game.