Can't be Europe (Germany '06)...
Can't be Asia (Japan/S. Korea '02) and Beijing Olympics...
Can't be South America (Brazil '14)...
This leaves only four options in my mind: Australia (enough stadiums, but they are meant for rugby, plus not enough market draw), Morocco (finished 2nd in host voting in three of last four World Cups), Mexico (large enough stadiums, and great market draw, but probably couldn't organize within one year), and U.S. (probably the best at organizing, lack of big enough stadiums, unless some football stadiums constructed wider field sizes, decent market draw, and IMO would draw most international fans).
I know this scenario is extremely unlikely. However, what if Atlanta or Charlotte hosted some matches...