"Double Cast"

[Doombringer]

Agreed. Still think it would cool and mildly useful, but I'd go for something like ManaKing's Firesword/Icesword first. I always thought Runic would be good for this. The Runic JA would absorb the next elemental spell cast by the RDM, a mob or a party member, then lets you unleash its power with enhanced damage on your next WS. Ideally you'd be able to double just the nuke power with the release, in addition to the WS damage. You could use your own nuke, or a SCH or BLM in the party could enhance your damage by providing a higher tier spell for absorption than the RDM could.

that'd also be a pretty interesting way for a blm to nuke hard without gaining any hate.