Note – this should be spoiler free, but it does talk about a line in the Sarah Jane Adventures episode that aired today in the UK (part 2 of “Death of the Doctor”), so if you don’t want to be spoiled about a line irrelevant to the plot, don’t read on.
So it seems the entire Whodom universe got its knickers in a twist about a throwaway line, although that was helped by things that Russell T. Davies said in the days leading up to it.
It is well established in the Who universe that the Time Lords have a general limit of 12 regenerations. Why 12 is not explained, but it was a major plot point of several episodes, including the Trial Of A Time Lord series. It is also established that the Time Lords had the capability to grant additional regenerations, either outright (“The Five Doctors”) or by transfer (The Trial Of A Time Lord), or through great energies (several of the Master’s last regenerations). So it’s not a hard rule anyways that really needs to be addressed right now.
While explaining to Clyde about his ability to regenerate, The Doctor says he can regenerate “507 times”. But it is said rapid fire, and I don’t believe without any sort of seriousness. Yet I have a feeling it will be debated until the – ahem – end of time.
And in [warning – article may contain spoilers] Davies’ interview with SFX Magazine, it certainly seems like it was intended to be “cheeky” – but then he also seems to think that the regeneration limit isn’t actually all that important, and compares it to what was likely a similar throwaway line (or at least before the writers realized that they needed to be consistent) by the Third Doctor about being “thousands of years old”, and how no one cares about that “fact”.
Anyways, I think it is a grave mistake to attempt to resolve this issue long before it matters, as it itself can become a great plot point. The 13th Doctor (whoever he – or she 🙂 – is), sustains lethal damage, and is preparing to die, for the last time. Cue emotional scenes, old companions, etc. Everyone says their goodbyes, and he dies…and everyone leaves, and we think the series is actually over, for good…but something strange happens – he still regenerates! And he has no idea why, and needs to find out why the universe played the ultimate trick on him…
After all – there are many outs to the limit established, and infinitely more that can be invented.