What I always have thought Borderlands was missing was a way for Gear crafting. Even if it is as a money sink. Gear is already a collection of mods so it shouldn’t be hard to allow breaking down gear into parts even each part could have different rarities or values which then leads to more customisation.
If there was customisation like that is in the latest Cod it would be amazing building a gun for fun and craziness it would fit the Borderlands world and just be insane. Weapons could look very silly yet have cool function.
You could even restrict crafting to a certain location which then would store your parts in a bank there. While some creations may not be useful in combat you could still make things that are fun to use.