This is not the end, and the Moment was not prepared for

Tell me how you do a regeneration scene without doing a regeneration scene.
What if ... the next Doctor has not been cast yet, and Billie Piper is
 playing the Moment in a call back to the Watcher in Logopolis. The next
 Doctor then emerges from her at the start of the next episode.
This allows RTD to film Ncuti's departure before casting his successor. I'm
 currently hoping this is all a gimmick. Because I'm not sure I can cope
 with Billie as the Doctor - I'm still disappointed that they wasted Archie
 Panjabi as the Rani. She was top of my list for the next female Doctor.
--
There’s no point in being grown up if you can’t act a little childish
 sometimes.