Alidar Jarok wrote:
I strongly suspect that much of the plot was written after the major casting was known (so Moffat could adapt to either Eccleston or Tennant), but I tend to agree that Eccleston likely would have replaced Tennant rather than Hurt's Doctor.
Moffat admited early on that Tennant was always gonna be in it, being the most popular NuWho and all that. Getting Eccleston would've been a bonus - and there's the odd rumor that he'd had two scenarios planned out for the special, one WITH Nine in it, and one without. And we saw the latter one, obviously, if thats to be true.
I think Moffat wanted his own Doctor for the role. If it had been McGann or Eccleston, fans of those characters would probably have been upset at the dramatic character revision necessary to make the character work. It had to be someone with a bit of an unpredictability who was "different" from the other Doctors. Plus, an established Doctor isn't a secret (one he will take to his grave).
While I agree with you, I would still have liked it enormously if it were Eight instead of War Doctor in it. Not only because of prospect of Paul McGann in a meaty, full-center role, but because we know that Moffat would aknowledge the suffering that Doctor went through in the audios and would add them in his characterization accordingly.
Eccleston being in the War Doctor's place is also an idea I'd like, and he's my favorite Doctor, but I think it wouldn't make that much sense, unless he'd been recently regenerated before exterminating Time Lords and Daleks alike.
In the end, we still got a pretty good John Hurt as a Doctor, which if fine enough, really. But I wouldn't have been phased at all if it'd been either 8 or 9 in that role - in fact, it'd be more preferable, from a writing perspective.