1. The only Doctors I don't recall seeing in "The Name of the Doctor" are Tennant and McGann, though they may have been among the shadowy forms running around at the end.
2. Maybe the Anniversary Special will explain why Alien, in which John Hurt had a memorable role, is similar to The Ark in Space.
3. Sounds like Eccleston's refusal to appear in the special forced Steven Moffat to change his plans significantly. If someone came to you and said, "For the 50th anniversary special of this massively beloved series I have an intricate plan for which you are crucial. Are you on board?" why would you say, "No"? Eccleston must have really hated working on the show. It's hard to imagine working around Eccleston's schedule was the problem.
4. If the anniversary special does not include the Valeyard, what people are saying John Hurt does establish means that it'll be Matt Smith's Doctor who will have to contend with the Valeyard issue at some point unless it's decided to ignore the issue which, since the Valeyard's mentioned in "The Name of the Doctor", doesn't seem likely. One of the reasons, also, it would be nice to go back to that story is because it was the last one on which long time writer and showrunner in the mid-70s, Robert Holmes, worked, his death preventing him from writing the second half of The Ultimate Foe, the last serial in Trial of a Time Lord.
I always thought the long term plan was to have the Seventh Doctor save the Doctor from himself. Yes, I'm still holding out hope Sylvester McCoy will appear at some point.
Speaking of the Seventh Doctor, Lady Peinforte, in Silver Nemesis, knew the Doctor's name and threatened to reveal it to the Cybermen. The Doctor's flippant reply that she go ahead, and the Cybermen not caring at all what the Doctor's name is, is even funnier now.