Indeed, there are two particularly exciting possibilities, and it could actually be both. Or neither.
So, for one thing, I've heard repeated, low-level talk that all of the Doctors* will make some kind of appearance in the main 50th episode. I'm not taking it for granted, but if it did happen, this may have required some new filming from McGann.
Or maybe it didn't, because… well, I was first told months and months and months ago of one way that old Doctors would appear in the episode that wouldn't require any new filming on their part or the use of any old footage. More on that later at a later time, I think…
Concerning another McGann prospect – and this is the more interesting possibility, I think – I did, some time ago, get a tip-off that the actor will appear in a minisode prologue to the 50th special, and that this little film would feature his regeneration into John Hurt's form. The idea, I heard, was for this to drop sometime in early November, either on TV, in cinemas or on the BBC website. Or all of the above.
At the time, I was sceptical, but more information has come to light recently which firms up McGann's involvement in… something. And that something could very well be the minisode.
I'll keep digging.
*All 53. Okay, just 52 of them, but that's close enough, right?