Moffat and Gatiss hinted at what’s to come for the two detectives in the new episodes. For starters, Moriarty will “be featured in the new season,” and Moffat reiterated that their plan to bring him back (after teasing his return during the series 3 finale) had been set in stone for a while.
THR says the creators also teased bigger roles for the women of Sherlock. They reportedly suggested “the show is likely to see increased roles for female characters Molly Hooper (Louise Brealey) and Mrs. Hudson (Una Stubbs).” In addition, new female characters “could” be added. Moffat and Gatiss did not offer specific details, as the show is historically very secretive about future plot lines.