Jack Could Come Back

Since his initial appearance in Series 1 and return in Series 3, the return of Captain Jack Harkness has been the subject of much debate. Steven Moffat has given some insight into the subject:

"When we've got a good story, we'll do it," he says. "You can't just bring somebody back and say 'that's a story'. I'll be thinking, 'you know what this needs? We need to bring Jack back for it.'"

 He also told how he had plans to bring back for A Good Man Goes to War, but was unable due to filming for Torchwood.

 “I’d have [brought back  Jack] for ‘A Good Man Goes To War,’ because it’d be obvious for him to call upon Jack in those circumstances,” says Moffat. “But John was busy doing Miracle Day.” 

And on the Doctor ever coming to Torchwood:

“The Doctor could never go to Torchwood,” Moffat says. “Russell [T Davies] and I both agree on that. Doctor Who has a tremendous relationship with children in Britain. They’d want to watch Torchwood then, and it’s not really a children’s show.”