Crafting
Announced alongside the Glave is a new crafting system, fulfilling a request from Guardians that has existed from Destiny 1. While details are extremely scarce at the moment on how the crafting system in Destiny 2 will actually work, we do have the below brief description via Bungie and the above photo to speculate about.
Master the new crafting system and create custom weaponry with unique combinations of mods, shaders, and advanced stat pools. When fighting a god, leave nothing on the table.
via Bungie
We do know from the live stream that it will utilize some kind of EXP system where you use your gun in combat. It will level up and that will allow you to advance and upgrade it in some shape, way, or form. Whether or not you can truly create your ultimate god roll is still up in the air.