I cannot do this because honestly i'm clueless when it comes to modeling and scripting, but my suggestion is that, someone (anyone) should make a (Somewhat-big) Pack of parts of (real or imaginary) gun/weapon parts, like handles and blades, hilts and guards of swords/melee weapons, and grips,foregrips, lights, sights, stocks,colors, etc... of gun models and make it all in one pack and you can collect parts and interchange them on a weapon, and even name/save your created weapons to the server, and to make customization easier, include a GUI to help with it, and have the GUI give a preview of how your weapon will look.
Now as i said before, dont count on me to make this because i said i'm completley clueless when it comes to scripting or modeling, but anyone that feels like taking up the challenge can do this, and just to keep this post alive, why not post pictures of cool parts or whole weapons you'd would love to interchange with one another.
Even if this never becomes a reality, isn't still a nice thought?
Summary:
Customizable Weapons,
Melee:Blade, Handle, Hilt, Guard, Color, Hammer Head, Axe Head, Point
Ranged: String, Bow, Thrown, Shot, Ammunition, Body, Stock, Sight, Etc. atatchments (Laser pointer, Flashlight, foregrip, etc.), Barrel, Grip/handle, Clip, Strap
If you have any other idea's as to what you could add to this, Please, I encourage you to.