I had a thought the other day (it happens sometimes), and its based on the introduction of dual-wielding in Skyrim. Basically, Skyrim is a likely precursor to Fallout 4, and because of that, I'd be amazed if dual wielding wasn't included, at least in some form.
And you know what, I don't want it. It looks cool, but it would completely throw the entire concept of weapon balancing and perks out of the window. In a FPS, its fine, but in a RPG game like Fallout, I don't think it belongs.
Also, on another level, dual wielding suffers horribly due to the UI. Basically, hotkeying items is nigh on impossible when you have two hands to cater for. That's why the 'Favourites' menu appeared in Skyrim - to allow you to assign commonly used weapons to each hand. Fine, but it accounts for an extraordinary amount of game time spent in menu screens, rather than switching weapons on the fly.
Just my two caps.