I like the idea of endgame, high end items, I think you should need to research them through the xp system and have to find rare materials to craft them.
different kinds of ore, specific types of wood, cloth, etc. could be necessary for said items.
Custom items and guns would be explosively popular too if added, this is whyI am all about making the weapon crafting system modular, kind of like fallout 4. Each weapon would be personalized and it would create lots of incentive to not die and lose your gun.
I guess you could find the legendary items in loot drop boxes too, but to craft them it should require a certain amount of effort on the players part…