As things are appearing, I have this image of what the 2nd headquarters will end up being, and it's probably way different than people suspect. The odds of DC being picked now? It's about a 99-percent chance.
I think Amazon is really building a corporate place that has limited personnel (probably no more than three-hundred folks) and will be this lobbyist-like element for the corporation.
I believe that Amazon will walk in....probably buy the Newseum structure that sits between the White House and Congress, and turn it into a public structure. Forty percent of the structure will stay the same....the rest turn into office space or speaking rooms.
After the smoke clears, the public will come to realize that Amazon is trying to get various things stacked in their favor, and grow the company in massive ways. The thought that it would be a real headquarters? No. It's there in DC for a reason, and they intend to talk political players into decisions which benefit the company over the next century.