WARNING: Blog post contains hardcore Doctor Who geekery! Read at your own peril!
I was reading Charlie Jane Anders' review of the Doctor Who season six finale at io9, and was intrigued by her mention of something call the Cartmel Masterplan, which I had never heard of. Basically, late-1980s script editor Andrew Cartmel wanted to retcon the Doctor's backstory in order to restore some of the mystery that had been a feature of the series' early years. To this end, he decided to make two of the founders of Time Lord society, Omega and Rassilon, into contemporaries.
Omega was first introduced in "The Three Doctors", a 1973 serial which celebrated the series' 10th anniversary by bringing back Third Doctor Jon Pertwee's two precedessors, Richard Hartnell and Patrick Troughton. As revealed in the story, Omega was a legendary figure among the Time Lords -- so legendary, in fact, that he was widely regarded as a myth until the Doctors learned that he A) was real; and B) had been trapped in an antimatter universe for untold ages. Omega died at the end of "The Three Doctors".
Rassilon was first mentioned in "The Deadly Assassin", a 1976 serial where Fourth Doctor Tom Baker returns to Gallifrey to prevent an assasination. Rassilon himself was revered as the ancient founder of Time Lord society, and two relics associated with him, the Sash and the Rod of Rassilon, play a part in the story's finale.
Note the different ways the Time Lords viewed them. Omega was a mythical figure whom nobody believed had been a real person. Basically, he was the Time Lord King Arthur. Rassilon, OTOH, was a thoroughly historical person. In the 1980 serial "State of Decay", the Doctor is able to read a document written by Rassilon himself, and in the 1983 20th anniversary special "The Five Doctors" much of the action takes place in Rassilon's tomb. In other words, Rassilon was the Time Lord Alfred the Great.
So, you had a mythical Time Lord founder from a time of legends, and a historical Time Lord founder from ancient history. And that was a good thing. It gave Time Lord society a sense of depth. And then Andrew Cartmel had to go and spoil it by trying to make the two men contemporaries for no good reason. Fortunately, the original series ended before Cartmel could make his stupid idea canon, and the new series has killed off all the Time Lords except the Doctor himself, so the question is moot.
But the idea is out there. There's always the chance that executive producer Steven Moffat, or one of his successors, will run out of ideas for the show, and decide, in desperation, to bring this one back from the grave. I live in fear of that day.