BBC Insiders have supposedly told the Radio Times that the next Doctor's identity will be revealed just before the filming of the Christmas Special gets under-way this Autumn, giving the most likely months as August or September (despite August actually not being in the Autumn.....). It is also suggested that filming will go immediately start on the following series once the Christmas Special has been completed.
The announcement would echo the way the BBC announced that David Tennant was returning for the 50th Anniversary.
So if this news is true, we have at least 6 more weeks of speculation before the new Doctor is revealed. There was no mention of whether the new Doctor's introduction will feature in a Doctor Who Confidential-esque special like Matt's did.
The BBC originally hoped to begin filming for the Christmas Special earlier, however it was suggested that it had to be delayed, however a spokeswoman said that "[they] are completely on track." This could possibly be due to a late script. Again.