Since the SMG has already been confirmed, I'm actually just going to out and say that I don't think any non-Halo 4 weapons should make a return. Halo 4 has, by far, the biggest and broadest weapon sandbox of all the Halo games to date: the only weapons it doesn't have are the Plasma Rifle and Repeater, the Plasma Cannon, the SMG, the Sentinel Beam, the Rocket Pod, the Brute Shot, the Grenade Launcher and a few of the vehicles. Of these: the repeater was worthless anyway, the Rifle has been replaced, the Cannon did the same job as the Fuel Rod Gun but worse, the SMG is coming back, the Sentinel Beam was rare and ineffective, the Rocket Pod's AA role has been replaced by the Rocket Launcher, the Brute Shot is an ugly Concussion Rifle, the Grenade Launcher is essentially a Sticky Detonator, and the various vehicles, while cool, were just racial variants of things like the Warthog and Mongoose.
What I want to see are completely new weapons. Halo 4 had some really interesting new tools, like the Railgun, the Binary Rifle, and the SAW, so let's see more stuff like that. Let's have some new grenade types besides bouncy and sticky; let's have some new support weapons, rather than raw damage dealers; let's have weapons which kills crews without damaging vehicles; let's have a gun which fires Frag Grenades in rapid succession. We've already used things which have been in previous Halo games, let's have some new weapons to learn to love and fear!