Dual-Wielding looks cool, but it's a gimmick honestly. Think about the weapons you are dual wielding. Dual wielded SMGs are very powerful dual wielded, but severelly weak when you only have one. Just beef up the smg itself, and that problem is eliminated. No need for dual wielding. The noob combo stated above is also a problem, especially if you spawn with a magnum. Find a plasma pistol, easy kills. I mean think about the weapons you could dual wield.
Needler: It's a power weapon now, not going to work.
Magnum: very strong by itself. Could kill a player in about three-four (six-seven) shots if it was dual wielded.
Plasma pistols: Help everything else out by removing shields, pretty weak when two are dual wielded together at the same time.
SMGs: already stated above.
Boltshot: Can't really make a shotgun blast be any more one hit kill then it already is, it's not like dual wielding increases range, which is the boltshot's main problem.
Bottom line: Dual Wielding forces many weapons to be weaker alone than they ever should have been.
Like I said though, it looks cool, and that's why people really want it back. Wouldn't mind having it in Campaign, but they are not going to add that for a one gamemode and restrict it in others.