This is not so much a new mechanic as a few ideas I have for improvements to the crafting system/weaponry/armour in Fallout 4.
After many hours of playing Skyrim,Vegas,and roaming the Capitol Wastes, I feel that the crafting system is lacking.Skyrim(while obviously unrelated to Fallout)let you improve your weapons/armor, but there was no visual difference between a normal steel dagger,for example, and a legendary steel dagger to show how it suddenly gained several more points of damage.I would like to see this in the next Fallout,but better.Guns(unless bought new/relatively new from groups such as the gun runners) should be dirty looking, with tape,bolts and screws holding it together.Over time as you upgrade your weaponry with newer parts,better materials,etc., the appearance(and damage,dps,weaponhealth,etc.,) will clearly improve.This can apply to Melee Weapons as well, e.g. new blades,lightweight materials,blahblah.Weapons should over time(in my opinion) get dirtier as you roam a dusty wasteland.It dosent make much sense that my weapons remain sparkly clean for years.Even a simple cloth in your inventory would be better than this.
Armour could use this mechanic overhaul as well.Being able to treat and tan leather from hides(much like in skyrim) and patch up your leather armour or welding armour plating on to your dirty business suit would be two examples of this.Being able to create custom armours and weapons would also be good,i.e. scratching words on the side of your gun,adding little bits of nothing, like wrapping your gun in Nuka-Cola Wrappers,hanging a faction's flag on the barrel,or even the simple pleasure of wearing a belt of hammers over power armour.Speaking of, having an optional feature to "power" your power armour with fission batteries to reach its full potential,as it never seemed to live up to what it promises,and could be easily dealt with with some AP rounds.Okay, I'm done blathering, thanks for reading my entry.