This is half a question on whether anyone has ever done this or if it's ever come up in cannon, and half a question on what people think of it...
The description for the powers common to dragons goes as follows:
QUOTE (SR4 @ pg296)
Innate Powers: Dragonspeech, Dual Natured, Elemental
Attack (usually Fire), Enhanced Senses (Enhanced Smell,
Low-Light Vision, Thermographic Vision, Wide-Band
Hearing), Hardened Armor 8, Mystic Armor 8, Natural
Weapon (Bite/Claws: DV 10P, AP –2), Sapience
Individual Powers: Animal Control, Compulsion, Corrosive
Saliva, Fear, Influence, Noxious Breath, Venom.
Attack (usually Fire), Enhanced Senses (Enhanced Smell,
Low-Light Vision, Thermographic Vision, Wide-Band
Hearing), Hardened Armor 8, Mystic Armor 8, Natural
Weapon (Bite/Claws: DV 10P, AP –2), Sapience
Individual Powers: Animal Control, Compulsion, Corrosive
Saliva, Fear, Influence, Noxious Breath, Venom.
Note the "usually Fire" under Elemental Attack. I don't remember ever coming across a dragon in the setting that used something other than fire for its breath weapon - I'm pretty certain none of the greats in DotSW are mentioned as having anything else, but it's a vivid idea. I can see Leviathan's with Elemental Attack (Sonic) which could be pretty nasty underwater. But Blast, Electricity and Cold would also be pretty dramatic.
The only advantage I've taken of the above quoted section is to have a feathered serpent with a sting in its tail (venom). Has anyone else had any Blue, White, Green etc. dragons in their games?

-Khadim.