While this may not be accepted in the main game I can almost guarantee someone will eventually mod something like this into the game!
But yes, fancy trinkets for all your guns, things like the "
" for ballistic weapons! Or maybe a Plasma Grenade Launcher of gooey death? The generic but classic Scope for weapons (better accuracy?), the magical tactical flashlight that can help in those pesky night time missions! Bayonets for whatever possible melee you could find yourself in, the list goes on and on! Balance will have to be tightened significantly to implement this obviously in addition to all the additional art needed and thus probably not going to happen.