“Items can have randomized properties associated with them which are currently used for clothing colors/patterns and holographic sight reticules/colors. This will open up a lot more customization options like harvesting plants to create dyes for your clothes (potentially paints too?), and make content creation a lot faster – in 3.x there are 8 versions of each item for each color which is a nightmare to maintain.”
from: Unturned II Devlog #004 – Smartly Dressed Games Blog
If some form of cosmetics were implemented into 4.X, they would likely use this system. Maybe alternative color or pattern options for items could be bought, earned, traded and/or gifted.
In addition to color/pattern variations, it might be neat to be able to add patches or something similar to clothing and some sort of markings to weapons/attachments.
Burlap, ghilie netting, paracord, etc. wrapped around weapons might be better suited as attachments than cosmetic variations, but I’m not sure.
I should also mention these threads (which may or may not be super dated when you’re reading this) as inspirations.