Does no one else agree that the Doctor being immortal would undermine the show?
Depends on how you define "immortal." It would certainly undermine the show if there was no longer a possibility of the Doctor being fatally injured before he could regenerate in the course of an adventure.
But I don't think that it undermines the show if the Doctor were to be otherwise immortal. Really, the show has already made him de facto immortal simply by virtue of the fact that they don't really address the idea of a regeneration limit and by virtue of having already made him so much older than all of his human companions. If they were to slip in a "the destruction of the Time Lords lifted the artificial limit on regenerations, rendering the Doctor immortal barring injury" infodump, it wouldn't realistically change any of the show's thematic content. It's already fundamentally a show preoccupied with the idea of how an immortal man copes with living in a universe of comparative mayflies.
How can there be an artificial limit imposed by the Time Lords in that way?
I don't know or care, because that's completely missing the point.
The point is that the show is already effectively about an immortal character, because the idea that the Doctor has a limit to his regenerations has never played a role in the program since it was revised, and that, as such, it would not weaken the show if they were to make the decision to contradict or remove the "13 regenerations" limit.
Saying that the limit was artificially induced by the Time Lords is just one potential justification for the decision to go beyond the Thirteenth Doctor. There could be others that they could use to justify the decision to maintain consistency. Or they could choose to ignore the inconsistency with TOS entirely. Whatever; it's not important. What's important is, it wouldn't weaken the show because the idea that the Doctor is mortal is already absent.
In fact, that line's just the kind of outright nonsense RTD would write. It cheapens regeneration, it cheapens the character, and it cheapens the mythos of the show.
You're getting caught up in irrelevant plot details instead of addressing the question of thematic content. Again, the specific plot device used to justify moving beyond the Thirteenth Doctor is irrelevant to the question of whether or not it weakens the program. Plot exists to serve theme and characters, not the other way around.
We've known about this limit for a long time now, and it's been a central part of the show.
No, it really hasn't. It was peripheral, at best, on TOS, and it's been completely absent from the revival.
Extend it in a clever way if you can find it, but I think making him immortal would be wrong all round.
Fair enough. But I think that's a very subjective evaluation; the most reasonable argument I think you can make is that the revived series has already been diminished from TOS by the Doctor's mortality being absent as a theme since "Rose" aired. But I don't think you can argue that contradicting the limit would weaken the series as it currently stands, because of the very absence of the idea of a regeneration limit since the revival began.
Even though it makes no sense,I got the impression he was just throwing Moffat something to use or not use. I prefer the unlimited regenerations due to no time lords.
I for one really don't care if it makes "no sense," because I don't care if they contradict an episode or two that aired before USENET was invented.
and over the possibilities of a cohesive and interesting story on the matter?
There are possibilities for cohesive and interesting stories on the opposite matter, too. There are possibilities for cohesive and interesting stories on almost any given subject. At the end of the day, this argument is completely subjective. The only question is which potentially cohesive and interesting story you subjectively prefer.
"They only said 13 once or twice."
How many times do they need to say it before it becomes real?
Um, never, because it's all equally fictional.

And RTD makes a valid point when he says that some "facts" stick and some don't. The Third Doctor claimed to be thousands of years old, but no one buys that anymore. Even the oldest estimates only put the Doctor at around 1,400.
Yeah the one thing that bothered me about the Master's resurrection in "The End of Time" and his "kewl" powers is that it was never really explained why they had to go through that elaborate ritual. All that was stated was that his DNA was contained or whatever in his ring and they needed a human to complete the ritual. I think it was a little complicated and convuleted process. I understand that there was no body for the Master to regenerate from and yes if he does return in the Moffat era it will be interesting to see how it happens.
The Master's resurrection scene in "The End of Time, Part One," was literally the first and only time in the RTD era that I sat there and shouted at the screen, "WHAT THE FUCK IS THIS SHIT?!"
But, hey, it's RTD, right? So, what everyone has done before is irrelevant. Right?
Yes.
(Of course, RTD is a hell of a lot more reverent of TOS than I would have been in his place. I'd've been tempted to declare all of TOS out of continuity with the current Who and to never feature any crossovers with TOS characters at all.)
Certainly it's trivial! My point was, just because RTD tried to change it on a whim doesn't mean it matters. There's a lifetime of the Thirteen limit in the show Doctor Who, and a single, joking line of RTD's in a spin-off kid's show. So, it's irrelevant what he said...![]()
Yep!
Everything that comes before now is irrelevant in comparison to the needs of the story being told now. If Moffat produces a story that requires the Doctor to have a 13-regeneration limit, then RTD's line in Death of the Doctor is irrelevant. If RTD had needed to write a story about how the Doctor has no regeneration limits, then all of those stories from TOS would have become irrelevant.
After all, it's just as irrelevant that Jack disappeared into the TARDIS in the Hub in "End of Days" but had to run for it out in the open in "Utopia." It's just as irrelevant that in "Voyage of the Damned," the Titanic was a threat to the whole planet yet in "Turn Left" it only destroyed southeast England. It's just as irrelevant that Martha would not be working at UNIT Base in New York at 4:00 AM Eastern Time on a Saturday just when the Earth happens to be transmatted to the Medusa Cascade at 8:00 AM Greenwich Time. It's just as irrelevant that....
Etc.
Besides, RTD made it pretty clear he doesn't think we should take the "507 regenerations" line too seriously.
There’s a fascinating academic study to be made out of how some facts stick and some don’t – how Jon Pertwee’s Doctor could say he was thousands of years old, and no-one listens to that, and yet someone once says he’s only got thirteen lives, and it becomes lore. It’s really interesting, I think. That’s why I’m quite serious that that 507 thing won’t stick, because the 13 is too deeply ingrained in the public consciousness. But how? How did that get there? It’s fascinating, it’s really weird. Anyway, that’ll be my book in my retirement!
Assuming RTD is the one who said that, I don't understand what he's talking about. Is he saying that because we don't bitch loudly that he changed the Doctor from being thousands of years old to "900" that we don't "listen" to that? What? HE'S the one that changed the age rule in the first place!
No, that would be the writers who had the Fourth Doctor and Romana running around saying that the Doctor was only around 700 years old during the Tom Baker era.
What RTD said is completely valid: "Facts" get put onscreen, and both later writers and fandom accept some facts as binding while ignoring others in favor of contradictory "facts" given later on. Which "facts" are accepted and which "facts" are ignored is often quite arbitrary and subjective.
And that was forty-years-ago, and there was no internet. So, how would he or anyone else know who bitched about what, when that happened?
Umm, the Internet is not the source of all fandom nitpicking. It existed as far back as the 1960s when people would write compendiums to their favorite TV shows and nitpick minor continuity glitches.
And why should the fact that a few fans like us are weird enough to ramble about the show and look up "facts" from the show on the Internet bind the producers? Their goal should be good storytelling, not pleasing nitpicky uber-fans like us.
RTD's just pulling it all from his ass...
This is the guy that basically said he just makes things up off the cuff
"I live in the moment!"
http://www.sfx.co.uk/
Discussing re-watching a repeat of “The Sound Of Drums”, he ponders the fact that you suddenly learn about things like the Archangel network, the Valiant, and the TARDIS becoming a Paradox Machine out of nowhere, with no advance seeding or foreshadowing in the script. It’s a fascinating passage, worth quoting at length: “I can see how annoying that looks. I can see how maddening it must be, for some people. Especially if you’re imposing really classical script structures and templates on that episode, even unconsciously. I must look like a vandal, a kid or an amateur… The simple fact is, all those things were planned. All of them were my choice. They’re not lazy, clumsy or desperate. They’re chosen. I can see more traditional ways of telling those stories, but I’m not interested. I think the stuff that you gain from writing in this way – the shock, the whirlwind, the freedom, the exhilaration – is worth the world. I’ve got this sort of tumbling, freewheeling style that somersaults along, with everything happening now - not later, not before, but now, now, now. I’ve made a Doctor Who that exists in the present tense. It’s happening now, right in front of your eyes! If you don’t like it, if you don’t join in with it then… blimey, these episodes must be nonsensical
Um, no, what he's saying there is that he deliberately writes so as to create the illusion of there having been no pre-planning, so as to create the impression that everything is happening suddenly and unexpectedly. He's not saying he's making stuff up off the cuff, he's saying that he's writing to create the impression that it's coming off the cuff.
^
One of the more irritating quotes from the man. "I'm a revolutionary; it's your own problem if you mistake it for incompetence".
It is.
The reason traditional and classical script structures developed is because they work. Just chucking any old rubbish in is fundamentally unsatisfying,
For you. For others, it works just fine. Certainly the fact that Doctor Who's audience consistently grew during RTD's tenure, even as it won numerous writing awards, indicates that many others did find RTD's structural decisions satisfying.
Welcome to subjective taste.