Pistols, yes.
Doubled rate of fire
Doubled DPS
Doubled mag size
Halved reload speed
Halved equip speed
Less stability
Less accuracy
No ADS
No knife, just pistol whip
Antyhing else is a big fat no.
And dual weilding needs a LOT of balancing, since anything that brings up damage output in any significant way can easily unbalance the game in its favor.
With Dual-weilding, you get double Damage-per-Second and more mag size (and even more with High-cap mags). Suddenly, a Dual Weild Ritchie can incap everyone unchallenged. You need massive drawbacks to this pure boost in killing power.
How about accuracy on par with being knocked down all the time, and no zoom?
Why not? Add a new 'gun', double uzi's or tec 9's. 1 button to fire them. It can be 100% cosmetic and probably look pretty cool ingame.
That would be a good idea, similar to the dual wielding in Killing Floor.
Killing Floor allows you to dual wield 9mm handguns and Handcanons. However, this changes their zoom function from ironsights to just a slight zoom. Since KF has no crosshairs, these pistols turn from deadly sniping weapons capable of killing most enemies in a few headshots to spam-weapons with zero accuracy.