Let me just put this idea out there.
tldr:
turn the Weapon Inspect screen that we already have into something like this:


The intent is to give LESS reason to mess around in Inventory screens and be able to do more weapon customization in an immersive in-game way while looking at the thing in-game in-hand.
As little UI clutter as possible, i'm thinking just hotkeys (arrow keys, numpad, d-pad?) and maybe a list in the bottom corner (like in the furniture placement screen) with the commands listed, and once you can remember the keybinds have a toggle to hide that too.
Less UI = more immersive + less work = win win.
The keybinds should only activate once the inspect button has been pressed and the gun is held up.
I think tricky part will be to auto populate the options with compatible items that you got in your player inventory for the weapon in hand (primary and secondary).
This would go well together with Adaptive HUD (hides main UI for more immersive gameplay and less OLED burn in).
And one of the mods that tell you when a loot container is empty, so you don't even have to open every single UI screen to check = less UI clutter is the mission.
There is a mod that lets you chamber a round by holding Shift + R outside of the inventory screen (so you can load a bullet and shoot it while not having a mag)... that is in the same line of thinking, doing something outside of the inventory.
And you can already hold CTRL + Mousewheel to move the scope along the top rail of the weapon, which is something you can't even do at all in the inventory screen.
(something like that to freely place laser pointers, grips, flashlights would also make a lot of sense... i assume stuff like that will be added later during development or will be added via mods eventually).
I just saw someone on Steam requesting a mod to load the mag you got equipped with bullets one by one...
like the Moslin or the Shotgun you'd press CTRL and then click in each bullet until it is full, using the animation that pops up when you press V to check your bullet count.
That request just got me thinking and this is where my line of thinking ended up at.