I think it would be neat if there was a station on the outpost (or a crafting station) that would let you customize the looks of your weapons. This would make the weapons more unique to the player and would let them add their own unique touch to it. For upgrading the weapons: have another station on the outpost (or a crafting station) that would let you make the weapon stronger and the ability to change the element damage of the weapon. Anyone else like this idea?
Some of this is already done with mods (Weapon Combiner, Custom Weapon Upgrade System), but an all-in-one package would be great. In general, I agree that all weapons should be moddable in-game, or just plain literally be modular in nature. Shade Co barrel (element, accuracy), Graxis stock (energy consumption, firing rate), and that projectile fabricator(base energy consumption, damage, secondary ability) you just looted. And then all of them upgradeable to the max tier, so you can build your perfect weapons collection.