Of course this is all just my rambling as i don't have a single idea how EGC actually works and if you can modify it so deeply or if enemy squads even have a class of their own (quick response, patrol, guard, etc).

Now, for the attachments.
You definitely can duct tape a laser pointer or strap a bipod to a FN-FAL but optics would be trickier as it doesn't have any rails at all (in it's basic model anyway). [...] Basic optics like 2x and reflex could easily be ghetto-fit on weapons but more sophisticated ones need at least an original rail to be used through an adapter for precision or for sturdiness on weapons with more kick.

Also i should definitely ask AIM or 1.13 respectable mod crews why aren't night optics still implemented.

I think attachements are easy to control because each weapon is only used for a certain "periode" by the enemy. So if say that laser-pointers would not be accurate for WWII and earlyer periodes, I would simply deny the respective weapons the ability to attach laser pointers, and that way also deny the player the ability to, say, use his MP40 with a laser pointer he found somewhere on the map.