September 21st is the street date for an upcoming "Rayquaza VS Keldeo Battle Arena Decks" release. It's all conjecture at this point, but it is believed that these will be reprints of Keldeo EX and Rayquaza EX(not sure which one), similar to how Mewtwo EX and Darkrai EX were reprints in their respective Arena decks. These decks will presumably include some great competitive staples, as well as holofoil energy, coins, damage counters, and an instructive playmat.
I think one interesting thing about this piece of news is the fact that Keldeo EX will be included, suggesting that the Expanded Format will not be changing for the next competitive season. There were rumors on the fringes of of the Pokemon community concerning the impending rotation entertaining the possibility of Expanded moving to XY Base Set and up and Standard being Primal Clash up. While it was unlikely before, now it seems the chances of the Expanded Format changing are very remote.