From the Blizzcon art section:
http://media.mmo-champion.com/images...rtOfWoW009.jpg
We're currently in Season 14. In the game right now there are some achievements related to Season 15, and I think people assumed they were put in there as a "just in case" scenario if the expansion drags out. So I'll take a shot in the dark here and speculate that this means the expansion is still pretty far off and we'll have another season of MoP PvP.