The devs have made it abundantly clear that they will not give jobs unique limit break effects. If they did you would have a situation where specific jobs are taken just for their limit break in certain fights. They have said that 3.0 will feature unique animations for each job, however. So a SMN and a BLM will have a mechanically identical LB but the SMN one will likely summon something to do the AOE damage instead of dropping a meteor.

One exception I see is BRD though. With the introduction of machinist we should see a proper ranged physical LB introduced which bards could potentially share. I don't really see machinist getting thrown into the healing AOE LB pool and they can't use any of the others that we currently have as they aren't tanks, melee or magic based.