At the moment, it’s just speculation. But it’s awesome speculation based upon two very key tweets, one from “Doctor Who” showrunner Steven Moffat, and the other from Sopha Myles, who played the title character in one of the show’s best five episodes, “The Girl in the Fireplace.”
This, from Steven Moffat:
“Right EVERYBODY who follows me, go and follow @SophiaMyles - spin that fireplace. NOW.”
This, from the lovely Sophia Myles (who was also great in “Spooks”)L
“Watch this (fire)place. The plot thickens…”
What can we infer? At the very least, that the Doctor will have another run-in with Reinette, although it would mean that the Doctor would have to interrupt the timeline established by “A Girl in the Fireplace.” But with Karen Gillan leaving, I don’t think it’s a huge stretch to imagine that she’d become the new companion. She’d also be … perfect, except that it’d be weird seeing Matt Smith with her, after it was David Tennant who fell so hard for her. Alas, bygones. I’ll take Sophia Myles in any way we can get her.