I like the concept presented by the OP. Even regardless of the effect it may have on kills, I think it would be a good idea to implement simply for the realism it adds to the game.
If you've been keeping up with the devblogs, you've probably noticed they are looking to add things like gun holsters so you can tell just by looking at someone whether they have a gun on them or not. I think this is just as crucial as the backpack concept because it allows you to better assess how much of a threat a potential target may be to you.
If realism was what we were going for here, it would work something like this: Players would have an "equipment" GUI that includes not only armor, but slots for things like a backpack, belt, holsters, tools, etc. Then, instead of serving as inventory slots as they currently do, spaces in the hotbar would instead "link" to items the player currently has equipped, kind of like a shortcut. Think of how hotbars work on MMORPGs like AO or WOW.
In order to expand their inventory spaces beyond those in their equipment GUI, players would need to either start with or obtain a backpack, which they would have to "equip" in a backpack "slot" in order to carry. They could access its inventory with the same hotkey used to pull up the equipment GUI, then swap items as desired. I like the idea of a hierarchy of backpacks with space and benefits relative to their crafting cost. Maybe it could even provide some protection akin to armor. Small items and raw materials would be able to fit in a backpack, but large weapons and tools like pickaxes, bows, shotguns, M4, MP5, and rifles would not, and they would appear on loops, straps, or holsters outside the backpack if not "in hand" as they would be carried in special slots in the equipment GUI. For small weapons and tools like hatchets and pistols, they could be carried in the backpack, but would need to be moved into the equipment GUI in order to be used, as items stored in a backpack would not be allowed to "link" to the hotbar.
If a player wanted to "link" small tools and weapons to the hotbar for easy access, these items would have to be equipped in holster "slots," made available only by equipping a belt.
For example, imagine an equipment GUI with the following slots:
Head, Chest, Legs, Feet - Used for helmets, vests, pants, boots, as is currently in place
Backpack - A slot exclusively for a backpack.
Belt - A slot exclusively for a belt, which could "activate" slots in the equipment GUI for small tools and weapons requiring holsters. Higher quality belts would open up more of these slots.
Holster 1, Holster 2, ... etc. (I'm thinking a max of 4-6) - slots available for small tools and weapons like hatchets and pistols. Only when equipped in a holster can these items be linked to the hotbar for quick access.
Shoulder 1, Shoulder 2, ... etc. (I'm thinking a max of 3-4) - slots available to hold large weapons and tools when not in use. Such weapons and armor would be visible on the player's back. This operates on the assumption that such weapons and tools are always accompanied by a means to strap them to one's body. Even a naked man can tote an MP5 on a shoulder strap if he so chooses. Alternatively, the number of these slots available could be dependent on the backpack a player is using.
Further realism may even include "Pocket" slots (I'm thinking a max of 6-10), which are made available by way of pants or belt to carry food and other consumables for easy access. If Garry has his way with how reloading guns will work, you could make it extra hardcore by requiring ammo clips to be stored in these slots in order to be reload the weapon "on the fly."
If something like this is implemented, I would hope things like belts and backpacks, especially for the lowest tier, would be either part of a newly spawned player's starting items or be incredibly easy to obtain, as they would be essential to getting so much as a stone hatchet.
Edited:
I understand what you're talking about. The best solution I can think of is to develop some sort of server mod whereby it would disallow newly spawned players from dealing or receiving damage to/from other players, at least temporarily. This "PVP Timer" could be manually deactivated by the player and/or automatically deactivated after a specified time period and/or once they craft something. Alternatively, an event that would normally cause them to take damage (i.e. getting blasted with shotgun) could put them on a significantly shortened timer that would at least give them a chance to run away. I don't think most players would want to go through the work of killing a naked if it meant having to chase them several hundred meters.
I think neither of us would prefer to see this implemented in base game, but it would be a straightforward mod for servers wanting to show more mercy to recently spawned players.
Some servers do have a mod that makes you immune to pvp damage for a certain amount of time. It's deactivated once you shoot your weapon, i believe. No matter what the target is.. and that first shot does no damage.