No. There shouldn't be another New Vegas DLC. Lonesome Road summed it up quite well. That is if you took the time to listen to Ulysses, and exhausted the DLC of every bit of info it has.
Fallout 3 could use another DLC, but it would never ever happen. Bethesda is done with FO3.
Edit: If you don't appreciate the end of New Vegas and the way it works, then you'd might as well count out FO and FO2? The ending to Fallout New Vegas and how it was set up was that the Courier could make a LOT more of a difference in the Mojave than the Lone Wanderer could in D.C. With the way F.O.N.V is set up, there is no possible way you would be able to insert a Broken Steel-like DLC. If they did somehow, like a lot of the people here have said, it would entirely ruin the game.
Fallout 3 was a diversion from the rest of the fallout games, and if you only like it, and dislike the how the rest are set up, then you aren't really a Fallout fan. New Vegas is just following the example of the old fallout games, which I think were great and essential to the series