One can quibble about The Day of The Doctor technically NOT being a 50th Anniversary Special since there have been two gaps in new episodes (seven and nine years respectively) but people keep saying, "50th Anniversary", so I am not going to launch a war on the subject. Now with the special coming our way, I thought I would take a few minutes to look over what I expect to happen.
First, I think the title is all wrong. The Day of The Doctor comes right after The Name of The Doctor, and I wonder why the production team would give such a similarly-sounding title to two consecutive stories. Further, I have never understood the NuWho fixation on the Doctor's actual name being some universe-shattering secret. I remember when the Doctor was just a renegade Time Lord, not really any different to other Time Lords save for the fact he ran away from Gallifrey. Now he has turned into some quasi-divine being, one whose current incarnation finds bow ties 'cool' and name tags a unique creation.
I don't think the Doctor's actual name is all that important, and don't think it will be revealed here. However, we do have a few odds and ends.
First, we have the introduction of John Hurt as The Doctor. IF we accept this as accurate, we then have a skewing of the numerical system that was established nearly 50 years ago. Since Patrick Troughton took the role in 1969, we have had an orderly series of Doctors (Troughton, the Second Doctor, being the second actor to take the role, Jon Pertwee the Third Doctor, and so forth). With Paul McGann's one-off special he became the Eight Doctor, and NuWho has confirmed this. Christopher Eccleston=Ninth, David Tennant=Tenth, Matt Smith=Eleventh. John Hurt's presence screws all that up. Why?
It is understood this Doctor came at the time of the Time War, placing him between Eight and Ninth (or as I call him, Doctor 8.5). Was he the actual Ninth Doctor? If so, then we shift each succeeding Doctor by one, making Smith the Twelfth Doctor. Longtime Who Canon has established and confirmed Time Lords can regenerate twelve times, which would make Peter Capaldi the Thirteenth Doctor and thus, the last of the Last of the Time Lords. We also have established that the Valeyard, a villain from the Trial of a Time Lord season, is the incarnation of the dark side of the Doctor, who came between the Twelfth and final regeneration.
Is Hurt the Valeyard? If so, then it totally screws up with the chronology of time since how does The Valeyard, who comes after Capaldi's Doctor, get to destroy Gallifrey?
Oy, my head hurts!
In regards to the limit of regenerations, we can get around it by claiming that River Song (who is not a Time Lord) 'gave up her remaining regenerations' to the Doctor in River's Secret Part 2 (Let's Kill Hitler). I know NuWho insists River (the Doctor's One True Love...make me gag) has Time Lord DNA by being conceived in the TARDIS. Few people question the logic of this (if I was conceived in a car, would that make me a Ford?), but even if we go with this, we don't know how many 'regenerations' she has. She's used up at least four regenerations prior to turning into what she is (and already the whole River Song storyline has been torn to tatters), so does this human have twelve regenerations like the Time Lords? Does she have less? Does she have more?
I am fascinated to learn how Hurt's Doctor 8.5 will be handled. It may be a trick of the Valeyard, who can alter official history. If I were to predict something, I would predict John Hurt is NOT a Doctor.
One thing I am concerned about is the lack of acknowledgement to all pre-2005 Doctors. Again, we may be surprised, but so far only Tenth Doctor David Tennant and his Companion Rose Tyler have been officially recognized as returning. In both the Tenth and Twentieth Anniversary Specials (The Three Doctors and The Five Doctors) there were logical reasons as to why the Doctors were taken out of their individual timestreams and thrown together. We do have a logic of sorts in bringing the Tenth and Eleventh Doctors (they are within the Doctor's timeline), so we do have a reason that will bring other Doctors back (minus the cantankerous Eccleston and the reluctant Tom Baker). The first Three Doctors have passed away (although actors can be hired to play them, as they did for The Five Doctors), so that isn't a hindrance.
Should The Day of The Doctor either not acknowledge or give a passing nod to all six living ex-Doctors the episode cannot be called a 50th Anniversary Special. If it acknowledges only the eight years of NuWho or worse, be a celebration of Tennant & Smith only or primarily, it will be a slap in the face of all Whovians.
I won't predict what will happen (rumors are all around). I can only hope that The Day of The Doctor pay proper credit to all Eleven Doctors, not just Tennant and Smith.
Finally, will Capaldi appear? I'm going to say no (though nothing says Smith won't start the regeneration process at the end of the episode).
One prediction I will make is that should Doctor 8.5 be defeated somehow, it will restore Gallifrey, allowing more Time Lords to be brought back to life.
Despite myself, I am looking forward to The Day of The Doctor. I think it may be a celebration of the Tennant/Smith Era, I think the Hurt Doctor is a false Doctor, Gallifrey will be restored (though that renders a whole lot of the Ninth Doctor's angst idiotic) and the regeneration will begin.
Until we see the episode, these are all guesses. In some ways, I hope to be wrong.
* For the record, THIS is Romana I: a Time Lord who became the Doctor's Companion when the White Guardian placed her with the Doctor to assist him in finding the six segments of The Key to Time. Not only was she a Time Lord, but in many ways was a much more intelligent Time Lord than the Doctor.
This is Romana II. On the show, she left the Doctor in E-Space, and her fate was never answered.
Could she still be alive?
Romana and the Doctor's granddaughter Susan were the only people pre-River to pilot the TARDIS better than the Doctor...and both 'kept the brake on'.