I'm not necessarily against that idea itself, but I'm not super psyched about it, either. On one hand, the classes are meant to be more or less identical, with the key differences being based solely in the elements themselves. Honestly, if I could think of a way to differentiate them that was flavorful, mechanically sound, and easy to implement I probably would.

In other news, I've been thinking over the idea of creating Mages of the Caustic Soul and Lightning Heart. I'm considering taking out the chill or heat metal SLA that the Fiery Souls and Icy Hearts get at 3rd level, and replacing them with the following:

Abilities:
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Caustic Soul:
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Acidic Touch (Su):
At 3rd level the Mage of the Caustic Soul can coat a creature in a corrosive substance with a mere touch. A number of times per day equal to his Charisma bonus, the Mage may deal 1d6 acid damage as a touch attack. Any creature or object that takes at least 1 point of damage in this way must make a Fortitude save (DC 10 + 1/2 HD + Charisma modifier) or immediately be covered in acid. In each subsequent round, the target must make another Fortitude saving throw. Failure means that it takes another 1d6 points of damage that round. Success means that the acid has been shaken off. (That is, once it succeeds on the saving throw, it's no longer covered in acid.)

A character covered in acid may automatically remove the substance by jumping into enough water to wash himself. If no body of water is at hand, rolling on the ground or rubbing at the acid with cloaks or the like as a Full-round action permits the character another save with a +4 bonus.

Fiery Soul:
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Burning Touch (Su):
At 3rd level the Mage of the Fiery Soul can ignite a creature in horrendous blaze with a mere touch. A number of times per day equal to his Charisma bonus, the Mage may deal 1d6 fire damage as a touch attack. Any creature or object that takes at least 1 point of damage in this way must make a Reflex save (DC 10 + 1/2 HD + Charisma modifier) or immediately catch fire. In each subsequent round, the target must make another Reflex saving throw. Failure means that it takes another 1d6 points of damage that round. Success means that the fire has gone out. (That is, once it succeeds on the saving throw, it's no longer on fire.)

A character on fire may automatically extinguish the flames by jumping into enough water to douse himself. If no body of water is at hand, rolling on the ground or smothering the fire with cloaks or the like as a Full-round action permits the character another save with a +4 bonus.

Icy Heart:
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Freezing Touch (Su):
A number of times per day equal to his Charisma bonus, the Mage may deal 1d6 cold damage as a touch attack. Any creature that takes at least 1 point of damage in this way must make a Fortitude save (DC 10 + 1/2 HD + Charisma modifier) or immediately be frozen in place. The creature is treated as being Dazed for one round. In each subsequent round, the creature must make another Fortitude saving throw. Failure means that it is Dazed for another round. Success means that the ice has melted or shattered. (That is, once it succeeds on the saving throw, it's no longer frozen.

Lightning Heart:
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Shocking Touch (Su):
A number of times per day equal to his Charisma bonus, the Mage may deal 1d6 electricity damage as a touch attack. Any creature that takes at least 1 point of damage in this way must make a Reflex save (DC 10 + 1/2 HD + Charisma modifier) or immediately be overloaded with energy and held in place. The creature is treated as being Dazed for one round. In each subsequent round, the creature must make another Reflex saving throw. Failure means that it is Dazed for another round. Success means that the electricity has dissipated. (That is, once it succeeds on the saving throw, it's no longer overwhelmed by energy.

I'm not so sure about that, though... Also, I'm not quite sure what to give the Caustic Soul and Lightning Heart at 8th level, though I'm looking into it. Finally, I think I know what to give the two new guys at 10th level: the same thing, but with a different element, and just immunity instead of the elemental subtype. I'm afraid that this would make them too strong in comparison to the Fiery Soul and Icy Heart, but I'm kind of at a loss here. Any comments, good, bad, or indifferent, would be greatly appreciated.