Sling mods for rifles/smudges
You can be real tacti-cool!

Let me start this post off by saying:

Rifles and SMGs especially are criminally under-loved, compared to pistols.

Also, a back holster or transportation bag is just kinda...weird, and not very good for quick-response situations! My recommendation is that we create a weapon mod that can only be installed on rifles/smgs... the sling!

Now now, I know it sounds silly, but think about it. It could be a 10k-15k weapon modification that only SMGs, rifles, and shotguns support. It would allow you to wear your weapon, but still function in a @default-weapon capacity, so that if you're attacked, you get a message about snapping your slung rifle/smg into your hands. It would appear on your body like a normal holster, something like Slung across %N's chest is a %weapon.

It should also be noted that use of a sling in stabilization of a firearm is standard doctrine training for some national militaries.

Make slings stand out as a cheaper, more accessible option than expensive and occasionally hard to find existing options, by making them cheaper, more available and visible (You can't effectively hide a weapon on a sling stowed in a way that isn't obvious you're packing heat) and not having any protective qualities in exchange, so the two options are separate and tactically distinct options.

what about expensive quickdraw holster options for EVERY weapon class? something like an expert's quickdraw holster for pistol, or energized saya for katanas?

It seems like this would make the large and heavy high-power firearms quicker and more agile compared to the small and lightweight low-power firearms.

I do not get the point. An item is added but what is it really adding? The reason we do not see as many firearms is because they have additional steps to do the exact same thing a katana does but less effectively. I like the idea of making rifles and SMGs something that must be carried in plane sight instead of a bag, the idea of making them so they cannot be disarmed could be a nice perk, but for the most part they just need to have a clear, distinctive advantage to counter all the disadvantages.