I will now let you in on a dirty little secret: This is entirely codable, Spit could probably code it half asleep. However, the problem is not in coding, but in organisation. See, the only reason the nco kit got the function is because it is always in the same slot. Now for every other kit you would need to make tons of weapon clones and extra kits for every single "exception" to the rule, meaning a map that uses non standard kit setups. Every uninque combination means cloning one of the weapons, means adding a new kit, means changing it in the map files. And hten there are kits, especially in early war, where no real alternative exists.
All in all, it is a huge, mostly clerical and thus rather boring, task that nobody wants to do.