They tested dual-wielding on mythbusters, it's absolutely of no advantage. You can't shoot faster or better since the gating factor is not the gun (you can shoot semi-automatic pistols extremely rapidly) it's the ability to focus and aim more than anything, both of which are hampered by dual-wielding not improved.
I think you're forgetting the obvious solution of having tons of preloaded magazines strapped to you.
Single button magazine ejection, slam your Uzis down onto fresh 100 round magazines. Bonus points for an automated system that moves the next set of magazines into the perfect arms length position at your side for the next reload.
Two handed reloads are for chumps when you are fighting zombies. You would be the guy I'm standing behind to give me that extra few seconds while they're busy eating you. That way once I finish off your attackers I can pick up your freshly loaded (but unspent) gun. And triple-wield!!
The second problem is that ammunition is heavy and carrying an infinite amount of it increases your need for food and water in a world where your biggest threats are cholera a dysentery. And unless you want to find yourself among jittery poorly-prepared armed people, you can't just show up to Cabellas to steal more ammo.
There are a few examples of people using two guns with belt fed ammo at the same time. Mobility and accuracy suffers, but some times dumping thousands of extra rounds a minute down range is simply worth the sacrifice.
The other advantage of using two guns is you get to let one cool down while reloading the other which helps avoid melting the barrel. This eventually ends up with a Gatling gun. Which is arguably hexa-wielding.
How about shooting with the double wielded guns. Then simply dropping the second one to reload. That way you would get the extra firepower for what it is worth. Then you can go reload super fast after that.
Then pocket the second gun until the first runs out. If you've got a buddy, get the zombies coming through a fatal funnel. You shoot straight at the funnel while your buddy reloads the inactive gun. This allows you to maximize accuracy while the lead never stops flying down the hallway (until you run out of ammo).
P.S. In terms of raw cool-factor, it's hard to beat this: https://www.youtube.com/watch?v=3tEYcUSQDyw
I won't spoil it by describing it.