I don't think it would work at all, and I doubt we will ever see Blue Mage in FFXIV given the nature of content and abilities. Most mobs use the same skills/spells that players already do. And SE already said earlier (can't find the link, but if I do I'll attach it) that they never meant players to have access to mob-specific abilities. I believe they used Haste as an example of how that skill wouldn't work in FFXIV's trinity set-up without being OP, so it will never be a player spell. From a balance stand-point the limit in the number of abilities a job has access too would hurt as well.