The Problem with Red Mage . . .

[ManaKing]

I actually would say leave DW gained only by /nin or /dnc

That said, I'd vote for a new Job Trait.

main-gauche
Allows user to equip a parrying-dagger in their left hand. (sub slot)
Level 40 - RDM (10% Delay reduction)

Main hand must be a sword, this does give it available to all as /RDM however the only real jobs that /RDM either have native DW or can't equip Swords/Daggers

Seeing as we're depicted as a fencer, with main weapons being rapier's/épée and having B skill in both Daggers and Swords, etc it fits the image perfectly, also it allows for the additional damage, the 10% is so they can make it so Enhances "Dual Wield" Effect equipment works with it, along with a possible new category for equipment Enhances "main-gauche" effect.

http://en.wikipedia.org/wiki/Parrying_dagger

Does the parrying dagger give Parrying Skill?
Does this trait stack with Dual Wield so that if you do it while /NIN or /DNC you get further reductions?
If you main hand a Dagger (i.e. Mandau) and offhand a sword, do you still get the trait? What about rapier and epee type swords if not all swords?