I still don't see it likely. A lot of people think that Dark Knight HAS to come from Gladiator because DRK and PLD have always been the yin and yang of each other, but then we could argue that the same goes for White Mage and Black Mage. Yet, they do not share the root class, so why should DRK and PLD? True, Cecil had a shield and sword, but that, as far as I'm aware (forgive me, I haven't played IV in at least 15 years) that was deeply related to the fact that Cecil's plot rounded around him being both a Paladin and a Dark Knight. A change of weapon would've been off. Throughout the rest of the Final Fantasy series, DRK was always displayed with two-handed weapons. And I hope that is what it will stay as.