the DLC would take place on the same island and all cutting down the cost to make it. and they would just need to reskin a couple enemies, add some new weapons/syringes/skills and items to craft and obviously at least a few cut-scenes. the only problem i really have with a Vaas DLC is that when you see how a person falls into madness, its always underwhelming. Anakin/Vader is a good example of an established bad guys backstory being botched.
and they need to add a cheat mode thats unlocked after finishing the game (infinite ammo, god mode, enemy outpost can be reset). just stuff for fun.