dual wielding wouldnt make sense since this game is a medieval game, the only time dual wielding combat was ever prominent was in childrens fantasy books, have you ever known any powerfull armies having large ranks of dual wielding warriors jumping around like prancing girls?
dual wielding just isent a serious fighting style and would bring down the realism of this game and make it look courney, like how it has done to star wars
As far as i know, DW, is not what the witcher does, you could have a finisher animation where he uses his other sword, but that should be about it.
Second, DW has been shown in books of many fencing schools Books, Lets take notice that there are not many books of this kind.
Second no army could train a Solider for 8 years so he can learn to use 2 weapons at the same time.
its far esier to train them to use a mace and shield.
As far as dueling, DW, Sword and dagger, is common, DW 2 large weapons, is hard , you dont block ever, you parry and conterstrike in the same motion. Thats my expirience from 6 years of kendo practice.