Idk one idea I had that I thought was cool was well Ill explain it. atleast now last 10 years or so US and other western soldiers have had the ability to equip their rifles with optics that they like...
If I understand what you are asking about - it's the abilility to take a standard rifle and customize it with a selection of sighting systems, etc.
It's been discussed - no real way to do this on ArmA. ArmA2 not sure, but hard to do at best.
Btw..i 've seen it happen to ArmA 1 before.
The rifleman had a M16 (ironsight) ,and with "action menu" was a something like "Acog optics" and..voila. (and vice-verse)
The trick (as easily understandable) was the game via action menu replaces the str8 M16 with one +Acog.
The problem to put an "elcan" or other optics demands a HUGH weapons pack with different optics for EACH weapon..
and Personally..i dont have problem for a ACE2 7 or 10GB of space in my HD..