Aren't we already to the point where people are saying we have too many skills?
Plus, there would be a huge issue with balance.
For example, your Sage idea:
You would have a White Mage with Astral Ice, that would be an insane amount of MP recovery for a Healer, way better then Scholar's.
And then you could just slip on Cleric Stance, which increase the damage of your spells by 10%, and poof, instead DPS. Now add Enochian, Ley Lines, and Presence of Mind.