Actor Matt Smith has been chatting to The Guardian (interview in the player below) and revealed a few tidbits for Doctor Who Series 7 (due to air in the Autumn). So far there are "four or five scripts which look in really good shape." Regarding casting for the upcoming run of episodes, the current Time Lord says,
"I found out a lovely bit of news this morning actually, about somebody who's going to be in it. I couldn't possibly tell you, but it's exciting. You'll know him. Or her."