The writer behind such episodes as The Crimson Horror, Night Terrors and Cold War has confirmed that he’s signed on to pen two more. After rampant twitter speculation as to which two he would do, he came out with the following:
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
So, do we take that to mean one each, or maybe two next year? Who knows. I’m sure we will get more details as the premiere for Series 8 gets closer.