The Moscow rumor has almost certainly released in response to a report that London has been secretly been scouted as a back up in case Rio can't go. The idea is that most of London's venues would still be open for business so the prep work would be easy. There is even an historical precedent. London got the 1948 games because they were most able to put the games together on a rush basis after WWII.
I wonder, though, how quickly a city like New York could organize things. If, say, next week, Rio was hit by a meteor, how quickly could the Big Apple get things going? Let's look at what venues were required for the London games in 2012. Roughly, they had:
- An Olympic stadium that was used for athletics and the opening and closing ceremonies. New York has two major league baseball stadiums and the new Giants stadium. Any of them could be used.
- Four (I think) smaller arenas. These were used for activities like basketball and gymnastics and the like. A venue like Madison Square Garden would be comparable. New York City probably has enough of these spots on their own, but if you extend to Boston and Philadelphia, you can get this to work with existing basketball arenas alone.
- Football (soccer) fields. London used six of these scattered throughout England, Scotland and Wales. Again, you could easily find six NFL venues that are close to NYC. And if that's too far out for you, there are probably 50 college sites that would also work.
- Some place for the swimming and diving would be needed. I couldn't find one quickly with Google but I'd be surprised if a venue didn't already exist somewhere on the North-Eastern seaboard. Same with a velodrome.
- Then there are a bunch of miscellaneous things like sailing and marathon and beach volleyball. None of this would be difficult to find and build up.
I'm not saying it would be easy, but if Rio can't go in 2016, I bet that New York City could step in on a fairly short notice.