I love Stephen and I bet one of his episodes would be fantastic!
He did write one didnt he? For series three but he found out Rose wasnt in it and couldnt re-write it all for Martha in time, something like that anyway

You really should start putting sources on your articles. Some of us like to check these things back.

He was supposed to write for series 2 however he couldnt hit the deadline, so Fear Her was written quickly to replace it

wikipedia :The episode was an overcommissioned episode, which replaced a planned but unproduced script by Stephen Fry.[4] Early drafts of this episode were titled “Chloe Webber Destroys the Earth”, and later, “You’re a Bad Girl, Chloe Webber”, with one such draft having the episode take place on another planet

Due to Fry’s script being dropped, production of some episodes of the second series had to be rescheduled, with “Fear Her” being produced alongside “The Idiot’s Lantern”. The episode was filmed during late January and early February 2006, with the cold temperatures experienced during filming being explained in the plot as part of the Isolus’ endothermic nature. The majority of the episode, including exterior shots and Chloe’s home, was filmed in the Tremorfa area of Cardiff, with a majority of the remainder filmed in the Doctor Who studios in Newport. Dame Kelly Holmes, who was referenced in the episode, was considered for the part of the torchbearer, but was committed to Dancing On Ice at the time.