The irony is, when ROG/NIN was added to the game a lot of their weapons were actually taken from GLA/PLD, like the gladius type swords, so in a way ROG/NIN is the dual-wielding sword user. Thus, I hate to say it, but GLA/PLD will never dual wield swords (the big clue is PLD's Job icon, it's a shield, and that is what half your abilities utilize.).

And ignore GLA's Job icon showing two crossed swords - MRD's icon shows two crossed great axes and they can't dual wield either. It's a metaphor for 'crossing swords' with the enemy as a dualist in the Colleseum, not an indication you can dual wield.