I just saw a theory saying that Missy isn't actually the master but an opposite sex clone OF the Master (like Jenny is a clone of the Doctor). The amount of lengths people will hypothesise theories that defy logic (in Doctor Freaking Who) to justify why Missy can't possibly be a female Master is starting to get ridiculous and gah. Argh. Stupid fandom. Anyway....how 100% true is this theory? I think its 100% true. It makes sense.
Ugh, yeah, there’s loads of ridiculous theories like that. Another one I see a lot is that the Master just possessed the body of a woman rather than regenerated into one. The one you’ve come across strikes me as particularly preposterous. Jenny was a distinct entity from the Doctor. She had her own name, personality, memories, and overall identity entirely distinct from him. Missy, meanwhile, is the Master through and through. She remembers their childhood, maintains her name (merely modified slightly to fit her new gender), and overall acts much like the Master we’ve always had. The theory just doesn’t fit at all.
Death in Heaven is the culmination of Moffat’s long-term movement towards gender-change regeneration and a female Doctor (I tried submitting an article on that to DWTV, but it doesn’t seem to have gone through. If nothing happens in a week or so, I’ll try submitting it again). It’s got Clara, characterized as a female Doctor and even taking his place in the titles. It’s got UNIT, re-written as a female-lead organization (with Kate and Osgood essentially gender-changed classic Who UNIT characters). There’s been years of references to such regeneration, since Matt Smith’s first moments. And when Osgood correctly guesses Missy’s identity, she specifically uses the word “regenerated”. I know there’s death of the author and all that, but I think it’s hard to deny the authorial intent is that Missy is a female regeneration of the Master, and that it’s part of a steady move towards making a female Doctor possible.