I have no proof of this, but the guess all season has been that the game between KC and the LA Galaxy on September 13th would be moved to the Wizards former home of Arrowhead Stadium. There was speculation back in February that the Wizards could play two games at Arrowhead this season. And while nothing has been officially announced, it seems like Arrowhead is going to be the site.
Why, you may ask? It's because of some of the advertising that the Wizards are doing for this game against LA. The game is being advertised as "St. Louis Night" (at the end of this article). Now Community America Ballpark seats only 10,385 people for the Wizards games. The Wizards got 32,867 people at last years Beckham game that was Beckhamless. If the team wasn't going to be moving the game to a larger venue, why would they spend the time and resources advertising a "St. Louis Night" for a game that you know will sell out CAB without it? The Wizards have sold out CAB 3 times this season and to think that the draw of Beckham alone wouldn't be enough to sell just over 10,000 tickets in KC alone then you need your head checked. There is just no reason to advertise this game like this to the other side of the state unless you plan to move it to a larger venue.
All signs seem to be pointing at the game being played at Arrowhead. The only hiccup is the fact that the Chiefs play the next day at noon, but Arrowhead staff have done quick changes in the past, they can do it again.