That'd be pretty neat to be honest. Imagine Summoners being able to bind Sprites out in the wild as non-combat pets/minions with a spell. Or Warriors being able to smash boulders to enter caves or such. Or Dragoons being able to jump onto ledges you can't reach otherwise. Elemental NPCs visible only to WHMs could provide some interesting dialogue. Same thing with hidden Voidsent NPCs for Black Mages. It'd even go with that idea of Blue Mages being a, 'Professor of Monsters,' without ruining the class if that was just non raid/trial content.