Just a few weapon ideas.
Heavy MG
Grenade Launcher
Crossbow
Recurve Bow
Makeshift Spear
I'd personally like to see a few more power armor designs as well. It's hard to believe that the US (Or UC) was the only country to have power armor. I'd like to see a Chinese set of some sort considering the war was between US and China. A few of my ideas for power armor:
CS-20 (Chinese power armor - lowest quality)
CS-21 (Mid quality/standard issue in the Great War)
CS-21x (Experimental stealth build/Extremely rare)
CS-22 (High quality/Just became certified for field use)
TS-30 (Equivalent of X0 Power Armor/extremely rare)
Deep Sea PA (Deep sea diving suit/power armor)
Deep Sea PA 02 (Design upgrades/damage resistance)
MADD 5MM (US Marine power armor/built in minigun)
MADD nvdeT (US Marine PA sporting a Fat Man)
MADD LZR (US Marine PA sporting a Gatling lazer)
The MADD designs could be used as PA for the Gunners considering they don't have a dedicated set. It'd make since considering they generally take over old military establishments.
Talking design...
All CS-** models could resemble a similar look to T-** US power armor, but varying in the helmets and chest region. Helmets would have orange visors with a red/yellow paintjob. They'd look more primitive in design than its US cousin and with many exposed components. As designs progress from CS-20 to 21 and 22 the designs will get more sleek with less external components while sporting better looking red/yellow paintjobs.
The TS-30 design would look different entirely much like the X0 to the T series. It'd be extremely advanced and sport a different paintjob.
Deep Sea PA would simply be a Deep Sea diving suit with a Power Armor system included. It would feature water breathing, superior visibility underwater, and no radiation taken from drinking water.
MADD Marine Power Armor would feature a combat ready design with built in weapons instead of a right hand. Different designs would look the same with the appropriate weapon.
Feel free to take these ideas and modify them. Let me know what you guys come up with!