I think there are a few Federal Departments whose headquarters buildings could be bulldozed for a productive economic alternative. :)
I'd be ok with razing some federal office buildings, but I wouldn't be ok with razing everything on the Mall and turning it into a big asphalt parking lot for football fans to use eight days a year.
The Anacostia waterfront had some possibilities, but Jack Kent Cooke moved before the waterfront redevelopment was far enough advanced. The Nats and DC United have great locations. The Deadskins are in Landover kicking themselves.
Moving across the river to Poplar Point within easy walking distance of the Anacostia metro station would be an interesting choice. That area is starting to improve (even Barry Farms is being replaced) but it's early enough that a package could probably be put together at reasonable cost. The whole Anacostia corridor is going upscale over the next generation, and it would be neat to have all three stadiums anchoring the southern end. A far suburban location like Ashburn is the easy default choice, but anywhere on the periphery imposes nasty transit times on three quarters of the metro area.
In retrospect, the Redskins should have simply rebuilt at the RFK site. It was as central as could be, short of razing the Capitol Building and using the Mall as a parking lot; it had a metro stop; the parking lots emptied directly onto an interstate across the river and into a high capacity residential street grid on the Capitol Hill side. I've lived on the Hill since 1979 within walking distance of RFK, and Redskins traffic was never a problem. And lest we forget, at RFK the 'Skins had the best blimp shot in the league. I imagine smart people in the organizations regret ever leaving, but Jack Kent Cooke was an old man determined to see his Taj Mahal built before he died.