A prequel for the Courier. The main character is almost completely missing backstory. The courier has to have gotten training and survival skills from someowhere before being hired to transport the chip. As you level him/her, you are basically relearning some of what you already knew before getting shot by Benny.
No.
The choice to not include a backstory was intentional, and a good call. Not having a backstory allows far more freedom to play the character you want (...it is a role playing game, after all). Further, it prevents a fail backstory from being foisted onto you. The Fallout 3 backstory was just fail of the most epic proportions.
A kid wanders out of a vault looking for daddy, and suddenly has the combat skills to kill hardened murderers and mutants? How exactly can a kid with no training or armor be expected to take the wasteland head on? Yes, I know it's a video game, but this stretch is just too much. The bad ass wasteland warrior feeling Fallout 3 gave you was undermined by almost every line of the awful, awful dialogue and story that forces you to behave like a child lost in the mall looking for a parent. Leaving it open ended allows you to actually answer the question of how you can handle yourself in a fight in your own way.
...but I digress. Anyways! DLC ideas:
-Nothing huge, just widen the map out and add more locations and towns that have quests, companions, and lore up to par with the rest of the game. Bigger is better when it comes to quality content.
-Area 51, but with no aliens... it turns out Area 51 is where the president kept his sixbots hidden from his wife.
-More and better casinos. We got ripped off! No craps? No poker? Seriously? Epic fail, Obsidian.