Ok there is one quest in particular that was neat in BL1. It was the gun assembly. You would run to an area and collect weapon parts, turn in quest and get a weapon based on quest weapon type.
So as a re-playable quest/not-so-craft I would think a neat thing to implement would be weapon building.
Sure you don’t technically get to craft the weapon, however it should be able to fit in with current mechanics. It will be behind M4 as the weapon body you choose will be a random Rare(40% chance) Epic(40% chance) or Legendary(20% chance) with a GUARANTEED Class specific anointment to the character you are.
You choose the weapon you want to craft: Assault Rifle, Sniper, Pistol, SMG, Shotgun, Rocket Launcher. The quest then randomly chooses a Trial for you to run. All weapon parts for the quest will drop from mobs within this Trial, save the last piece which can only be received from the boss.
Turn in for your new anointed weapon. 1/5 to be at least a specific weapon type legendary that is anointed to your character! This quest is repeatable for all weapons types.
And I dunno charge 10-100 eridium for each time you take quest or something like that if we need to. Whatever.