But going with the Blue Mage example, class-specific abilities would be earned by clearing specific dungeons, or taking the attack from a certain boss, while as that class and having the soul crystal equipped. Preferably, these abilities would be at least thematically linked to the boss/dungeon, if not a direct copy of the boss's ability.

With this, each class gets differentiated from the rest and gets a unique set of skills distinct from its other job/jobs; and depending on how the job level is handled, you could feasibly skip the long grind to 60 and maybe even not have to expand the Armoury.

There's my idea. Discuss or add your own!