Now for the idea itself.
I have been playing with the idea of the playable character being pre-war. setting them on a secret moon base built by vault tec and robcofor the exploration of the solar system. But due to the war the scientists on the base went into cryo sleep and have been sleeping since until recent events in New Vegas, one of the ghouls rockets hits the moon base's power facility which knocks out the cryo chambers. You wake up a week later, the power is failing and the base is losing stbaility. All the other sceinetists are dead becaus ethier pods lost power compeltely.
The idea form there on is that the moon base escape is the pre-game 'training' that you get in Fallout 3 and Fallout:NV. The main storyline is that due to the fact you are a pre-war survivor and scientist, the various factions of the war torn wastes are after you for your knowledge and you must avoid them to return to the space programs main base which you still have access to as an employee. The factions are all near the base fighting over it and trying to gain entry wihtout any luck (the main facility is underground).
Eventually you will enter the base and gain access to tech and etc....and can decide which faction to side with and so on. That is the rough idea thus far. I will be working on more details and ideas in my private time. But if anyone finds this interesting I may share more and owuld be happy to discuss my concept.