Broken Steel ruined Fallout 3.
Here is how.
The idea behind project purity was to instantly give everyone in DC clean pure water. It was to make all the water in the Tidal Basin and Potomac River. Instead the BoS end up running it, sending the water out in barrels, making everyone slaves to the BoS if they want clean water.
Since project purity was going to instantly clean up all that water, the Enclave saw it as chance to kill all the mutations in DC with their water born modded FEV. It would have turned DC wasteland into "A Graveyard." This doesn't end up happening with Broken Steel.
This makes the Enclave's plot in Fallout 3 pointless. Which means there was no point for the Enclave being in Fallout 3 and therefore the whole plot of Fallout 3 was pointless.
Enclave manage to destroy Optimus Prime with a super space weapon that for some reason they didn't have, when the BoS attacked Project Purity. No matter what you do, the Enclave get destroyed.
Yeah I know there area lot of "gamers" out there that couldn't give a crap about a logical and coherent plotline. No many just want more stuff to shoot and loot
The only way to have play after the end is to scrap the ending just like Fallout 3 did and that would destroy the main plot and story of New Vegas.
There will be no Broken Vegas for New Vegas or any other DLC.
All good stories have a beginning, a middle, and an end.
This ^