The most interesting part of the whole rumour to me has been the suggestion that he's filling the function in the story that Eccleston would have if had agreed to appear. Add that to Rose's post-Apocalyptic outfit and it does raise some interesting possibilities that may tie in with the suposed Series Finale synopsis that has appeared.
Piggy backing off that.
Why haven't we seen any alternate universe doctors?
What if there was a doctor in Pete's World who still went back to Galifrey on a regular basis etc?
Is the doctor excluded from the multi universe concept?
The novels say that the Dictator
in Inferno was that univese's Doctor. Also, Coming of the Terraphiles says the Time Lords drafted their alternate reality selves to help out with Time War, and as a result the Doctor really is the last Time Lord in all the multiverse.
However, as far as the show goes, RTD was of the opinion that the Time Lords were unique to the "prime" universe therefore there aren't any Time Lords or a Doctor travelling in Pete's world.