Three seasons into the new run: "And then I turned into 90s popstrel Billie Piper for five minutes" <confused look>
is all it takes.
Christ, I remember when Tennant name-dropping Gallifrey was a big deal.
Stephen Graves
"Whoever takes over Who will annoy fans if they don't explain Billie's appearance" and "we're having problems writing a Bond script becauae we have to deal with him dying in the last film" are prime exhibits in the case for why "canon" must die.