Well fallout new vegas takes place in Las vegas. Area 51 is 85 miles from there so why not make it where we can go there? As for the story for it there are all kinds of ideas for it. Maybe when the war happened all the important people in american went there to be safe and there is a colony the or maybe the president is still alive being kept alive in a brain thingy. Then with all the alien storys about area 51 after the war the aliens took area 51 and it is some alien colony? There are all kind of thing i could image that could be going on there and i think people would have lots of fun exploring area 51 in the wasteland. One more thing, giant radioactive scorpions are cool but a little old what about spiders? that would be intense and fun taking down some radioactive spiders. Just thought of this what if the president is a ghoul and running around in the wasteland after his Bunker at area 51 became radioactive? Well there are some ideas I have really hope you think about it.

Won't be an Area 51 DLC.

One of the devs (Jason Bergman) posted in another Area 51 DLC thread that they wanted to do an original idea and not just another Mothership Zeta with aliens.

Why don't you use
this http://www.gamesas.com/index.php?/forum/124-fallout-new-vegas-dlc-general-discussion/