I’m not sure if anyone’s thought of this. But I think the lady at the end is River. I mean, paradise could be the Library computer she got saved in. She also refered to the Doctor as his boyfriend. A new different Doctor, why not a new different River? Also Matt Smith said he didn’t want to see Alex Kingston’s River go with Capaldi but Moffat kept the character and changed the actor. And I know you’re thinking: “How did she regenerate, didn’t she use up all her regenerations to save Eleven?” Well the Doctor got a new set of regens, why not River?
I hope you found this theory interesting and maybe even believable and if you did, please spread it around.