Most of these ideas have been suggested elsewhere, but this thread is about my ideas for implementing them.

1. Battle Rifle:
One thing I've noticed is that there's a bit of a capability gap between the rifle and the SMG. The rifle is excellent for long-range shots but so slow to fire that at close range, missing your first shot is invariably fatal; I could live with it being usually fatal, but that seems a bit much. The SMG, on the other hand, is brilliant at ranges up to about 30-40 tiles but a complete waste of ammunition beyond that.* Rather than buffing or nerfing one or the other, I'd like to see a fourth weapon added that sits neatly in between the two in terms of damage, recoil and range. It could even have a historically accurate 20-round magazine. I'm somewhat ambivalent about giving it automatic fire, and I'd certainly want a toggle between full-auto and single shot.

2. Heavy Weapons:

a. Machine Gun:
This one would be extremely tricky to balance. I'm thinking it'd fire rounds about as powerful as the rifle -possibly with severely nerfed damage to blocks- in 100-round belts, but would have utterly uncontrollable recoil unless fired while either crouched or standing in front of a two-block wall. (Not sure how practical the latter would be to code.) It should also have fairly low-zoom iron sights; the purpose of a squad automatic weapon is to force the enemy to keep their heads down, and hitting anyone is a bonus.
b. Grenade Launcher:
This one's a bit easier. Single shot, long reload time, basically a way of launching an ordinary grenade about half as far again as the current standard. A minimum arming distance would probably be a good idea, as properly placing one's shots would likely take some practice.

3. Sidearms:
Yeah, I know. But hear me out. First, I think sidearms should only be available by default to players who select one of the above heavy weapons and maybe the rifle, instead of grenades. I envision three pistol types:
a. High-capacity semi-automatic with mild recoil and fairly low damage. (Example: Browning High-Power, Beretta M9 or most other service automatics.)
b. Lower-capacity semi-automatic that trades greater stopping power for added kick. (Example: Colt M1911A1 and its many imitators.)
c. Revolver of equal stopping power to the second semi-automatic, but with a still-smaller magazine and a longer reload time. (Example: Webley .455 series, Colt M1917.)
If the revolver sounds like it has several drawbacks and no real advantages over the two semi-automatics, that's because it does. I include it for a specific purpose I'll go into shortly, and also because some people just like revolvers better, so why not? Each pistol's range should be about one-third to half that of the SMG.

4. Satchel Charges:
An item the player can choose instead of grenades that does considerable damage to blocks, but very little to other players and can't be thrown very far. Ideally suited for taking out the bunker with a particularly skilled sniper, or flattening your own defensive line once it's breached to deny the advancing enemy the use of it. Also ideally suited for griefing, but that's what votekicks are for.

5. Melee Attacks:
There's several different ideas for these, but I think the simplest way is having a melee attack for everything with varying degrees of effectiveness. With the melee attack triggered by pressing Alt or something, for preference; I'm sure everyone's accidentally clobbered a squadmate who spawns on top of them while digging a tunnel with the pickaxe!

6. Serverside Weapon Tweaks:
Now this is the biggie. Not just skins, in fact I really don't care if those stay handled clientside. There's two main elements tro this.
a. Limits on how many weapons of each type per team, or disabling some weapons completely. Half the players on the server picking machine guns would make for an extremely boring game, so maybe limit them to two per side for example, or you could even try some sort of Cops and Robbers scenario with pistols only for a change.
b. Custom weapon ROF, damage, magazine size and reload time for each team. This would enable server owners to do all kinds of interesting stuff. For example, suppose someone wanted to run a War of Southern Aggression-themed match on their server. They could disable every weapon except the rifle, set the magazine size to a single round each and make the reload time take ages. A World War One-themed scenario could have one side's rifles less accurate but faster to fire and only let the green side pick revolvers while the blues had a semi-automatic with only eight rounds per magazine. Someone wanting an ultra-realistic scenario could make a single hit to the head or torso with any gun instantly fatal. The possibilities are limitless.