I'm sure peopole have mentioned these items before. The silencers could make it interesting. The Scar would be nice with an extended mag. The more customization the better in my book. 
#Extended magazines / silencers options for certain weapons through progression
uncut stump
worldly jackal
pretty much 100% of the available weapons have additional magazines after you get a few hundred kills with them, same for silencers...
not to sound mean, but have you actually looked at the attachments that you can use with the guns or are you just theory crafting?