I really shouldn't speculate, but these big DW finales become an intricate puzzle, don't they, and none more so than this. You start putting together all the little tidbits you've come across in interviews and spoilers and finding a theory that fits it all. So here is mine - if you are avoiding the trailers for next week or, of course, Part One, read ahead at your own risk:
The human race has become the Master race. The Doctor has nobody to confide in other than Wilf and the bastard Time Lords are back big-time. And that's before we start on what's become of Jack after CoE. But I keep coming back to what Julie G said on the S2 sleeve notes back in 2006, that RTD hasn't a cynical bone in his body. And he's a showman, so whatever he does it's going to be (or at least attempt to be) something nobody on TV has ever managed to pull off before.
What have we got? We know he's very cagey about whether we actually get to witness a regeneration. That he still regards the Doctor and Rose as the defining relationship of his era, but it can't go anywhere until the difference in life expectancy gets tackled. We knew that the Doctor knows his number's up at least ten minutes before the end. We know that at some point he goes back to the Powell Estate to see Rose before she even met him. And we know from A Writer's Tale that (a) RTD always intended, at least until he wrote himself into a corner on JE, that Ten should go to Rose when he regenerated and (b) he never really felt the JE solution worked.
What would be more natural than for him to turn the whole thing on its head and give us a happy ending after all? I think he just might.
Okay, back to a little canon now. And the rumours that the woman in white is the Doctor's mother, who is called Penelope Gate by the way. I think both those names are significant. Gate is obvious, and Penelope has mythic connections with the Odyssey, the greatest of all tales of the age-old conflict between a man's need to wander and a woman's to commit.
It wouldn't surprise me at all if Wilf turned out to be the Doctor's father, or at least a figure in a good place to plead for clemency on his behalf.
And then there's the suggestions that we're heading for a reset. I think it's very possible (particularly given the Blogtor Who trailer, the one that appears to show us the final Council of the Time War or something very similar) that all this time the Doctor has been living in an unsustainable timeline. I can't predict all the details, but my hunch is that he only had to do one or two dodgy things (maybe the first was Pompeii, when he changed history a little at Donna's request) and the dam holding back the alternative timeline will start to fracture.
I really hope that the Doctor is given the chance to lay down his terrible burden of survivor's guilt, either by rejecting his people's values in favour of humanity once and far all, or reversing the genocide he committed. And I think he will be allowed a concession, as an act of grace and mercy, in return. That will be to return to Rose and have the one adventure he's never had, and the one he so clearly desires.
Of course, if the Time Lords return, it will be possible to travel between universes again. There's no reason why he couldn't return to Bad Wolf Bay in the TARDIS right after the sentence he didn't finish in Doomsday. Heck, they could have filmed the reunion four years ago. I wouldn't put it past RTD. He could then complete a human lifespan with Rose and then return to his role as general Big Damn Saviour of the Universe. He could even have a family.
I'm leaving 10.5 out of this, because presumably in the scenario I've just outlined, he wouldn't exist. Some people think the two of them will swap, which might be a good way to save Donna, among other things. Personally I still think Donna will be unlikely to survive, but we'll see about that. I hope I'm wrong there.
It may be that the regeneration doesn't happen until after Rose dies and Ten returns to the parent universe. And what unfinished business would he have there? Well, he might want to see Rose before she even met him, to ease the pain of their separation in her future by telling her that he loves her, and he will return to her. So he goes back to the Powell Estate and does just that, and she doesn't realise who he is until Nine regenerates into Ten.
It's even possible that Ten doesn't regenerate, even then. We still haven't addressed something that I have a feeling RTD would want to address, to protect the future of the franchise. How many regenerations has the Doctor got left, and has he used up a spare one? I'm probably speculating too far now, but just suppose Matt Smith wasn't the Doctor at all, but his son with Rose - bequeathed the TARDIS, his name and the best possible start in life - two parents that loved each other beyond reason, one human and one alien - as, if some versions of canon are to be believed, the Doctor had himself.
And if I'm wrong? Then I'll just have to write it myself.