It has been confirmed by the man himself that actor and writer Mark Gatiss has been commissioned to write two new episodes for Doctor Who.
To clarify. I’ve been commissioned to write two episodes of ‘Doctor Who’. That doesn’t mean they’ll both necessarily be in this season.
— Mark Gatiss (@Markgatiss) March 27, 2014
He also recently told Digital Spy that new Peter Capaldi’s debut episode would be “exciting and disturbing.”