The guns are the core of the game imo, and if I were to make any single sweeping change to the game myself, it would be how the gun loot system works as well as how they function.
Guns should jam. They should get dirty over time. They should require maintenance. They should be more modifiable. With all that, they should also be statistically unique from one another.
They have the rarity system, albeit a very simple one, but I imagine Generation Zero taking a page from borderlands, generating random statistics such as accuracy, cleanliness, durability, recoil, camoflage, etc. Finding a gun that you already have an exact copy of could then become a good find. Maybe we can strip components out and replace wear and tear on our current firearms, etc.
This idea could go all the way into scopes and other attachments too, such as generating different scope UI’s and dot sights with different designs and camos regardless of rarity.
Realistically speaking - if you were in this scenario with killer robots everywhere - you’re going to become a hell of a gunsmith at your safehouse. You will have a table specifically for maintaining your guns. Forget the bike rack. You won’t have a bike rack. You’re going to have a hell of a workbench for all your guns. You’ll also know that no two guns will fire the same. Some lean left, some lean right. Some fire deadon for 100 rounds before the sight is out of whack. Some jam more than others. Some reload louder than others. Some have better weight distribution than others. I think if the devs focused on guns for one sweeping and awesome update, it would change the game in a huge and positive way.
This would add a very interesting and dynamic layer to the loot system, which seems to get pretty meh as you progress.