From an interview last week blizzard said we would be hearing more about it soon, as in actual soon and not blizzard soon. 5.1 came out pretty much exactly 2 months after MoP launched so I am expecting something similar for 6.1, but, that's just speculation obviously.
They also said in an interview or a bluepost or something similar that they felt that timeline was too quick. They'll want the average guilds to be making headway into mythic before dropping the next raid on them.