As I was playing NewZ for quite a long time, things have changed. They added more skins and guns are more easy to find. Pain in the ass is trading. Typing on discord you are selling something and waiting if someone is gonna respond or you just spam on trading lounge to sell your item for an hour or two.
What I would make is just some sort of online market, where you can sell things, putting your own price and let time do the work. It was here once, but never fixed and then removed. For other players, it would mean that they can buy things from other players and it could be so easy to do so.
Another suggestion I would make is global inventory management. Not able to move my items in it, change position or unload the gun directly in UI at main menu makes it a lot more time consuming. If it is on purpose to have players spend more time in the game, then I understand, but none would spend like an hour every 2 or 3 days to sort his inventory to make it not look like garbage. I would add some sort of sort button that would stack all the same clips or the whole inventory. So many times I had an issue that one C-MAG had 100 bullets, another 100 bullets and they just won't stack at all. Another change would be an player-server integration. Why would server want connection for every change you make in GI. Instead I would let it just for client and when you are done with the inventory, then update changes. It would save a lot of time gearing up or putting guns in inventory.
Maybe my suggestion are a bit over the top, but it is for sure, doable.
ADD: Please make at least guns reloading at lounge instant so I don't have to wait for ages to load my guns.