I'm quite happy with the storyline explanation through dialogues.dat for now, but who knows, I might add stuff to make it more interesting...
Weapon modding probably won't be present as you aint gonna be combining anything.
Trap weapons wouldn't be too hard to add but I'm not sure if they'll be very useful.
If weapons could break I wouldn't be able to track of what weapons the player has, and this is useful for me to know what ammo will be present and when I'm gonna give another one. So probably no.
I had a random idea today, if I decide to keep it you'll be able to pop headshots with the sniper rifle. (One in something chance of it happening.)
If I can be stuffed doing it I might be able prevent blood from showing up outside the map.
Some weapon Ideas:
Possible flame thrower,
Arming some of the squad with tazors,
More Aleryon weapons,
Sword (Already there),
Bio-Explosive pistol (Already there, pretty punishing in combat),
SMG (might just be mini gun with different name),
Plasma Rifle (Not to be confused with the present plasma gun).
Might make shotgun marines gray like normal enemies,
Will probably have scientists carrying an anti-virus,
Will probably explain the massive amounts of enemies you encounter,
You ,MIGHT, repeat MIGHT, encounter very mutated easily killable scientists with... I'm gonna stop this idea now before I give a spoiler...
More ideas will be revealed as they are generated (unless they spoil my secret plans for the storyline)...