So we have fire, ice, and lightning that do raw elemental damage, but maybe the rest of the elements need their own transformations.

Air: Convert impact damage into a percentage chance that you'll knock the target down (prior to the strike) OR increase the balance while decreasing the suitedness of a weapon. For very large weapons, this could result in a flip (12 balance / 3 suitedness 2HE for example).
Aether: Convert the weapon to attack attunement and nerves rather than vitality. Armor piercing. Description would be a phantom blade of sorts.
Water: Convert impact damage into a percentage chance that the target will "freeze" and suffer a random stat penalty (shortish duration). One of Agility, Reflex, Strength, Stamina. They can stack with rapid strikes.

Also, the weapon can "empower you" when you strike if you're aligned to that element, much like TM spells.

In a perfect world, a mage would be shaping a lot for effects.