So here's a little fan-fiction.If I were writing Doctor Who right now, this is how I would pen the final series.
The Doctor, after a particularly traumatic adventure involving a fracture not just in time, but in the nature of reality, is flung through a dimensional rift into another universe. During the trip he is fatally injured and is forced to regenerate. However, he has lost a lot of his time vortex energy and undergoes his 13th and last regeneration, only to return in the form of a child.
The Tardis remains fairly battered as well, so much so that its chameleon circuit and dimensional dampeners are destroyed and its vast, coral-like true form is revealed.
The child Doctor wanders through this alternate universe, which he soon realises is merely a parallel reality to our own, but at the end of its life cycle: it is heading towards a Big Crunch. Most of the stars have gone out and only a handful of civilisations remain.
On his travels, he meets Dalek Nau. The Daleks have, like all living things, evolved throughout the millennia and managed to override their genetic programming. Eventually they too succumbed to the laws of nature and were guided towards altruistic and constructive behaviour. In an effort to redeem themselves in the eyes of history, they scattered throughout all dimensions, realising that their destructive programming was more likely to return if they remained as a collective hive-mind. Thus, there is only one Dalek per universe, acting as neutral observer of events. Initially sceptical, the Doctor warms to Dalek Nau and teaches it his own moral code which, he realises with shame, he himself had begun to stray from. Together they would have a series of adventures before the last of the Doctor's vortex energy would run out. Dying, and the Big Crunch imminent, he would charge Nau with continuing his work, upholding peace and valuing life throughout all dimensions.
The Doctor would then die, while this song played in the background.
Nau would depart for another dimension as the Universe finally imploded, before beginning anew with a second Big Bang.
And that's my 13th Doctor story. Let me know what you think :)
Thanks for reading,