5. River's Sacrifice
...or maybe it did. Perhaps
this is the true legacy of Melody Pond. It wouldn't even need Alex Kingston to come back, but she'd probably make an appearance, still telepathically connected to Clara and explaining to a newly-regenerated Doctor why he's 55, Scottish, and not dead. (No anti-Scotland jokes about life expectancy, please.) Knowing how much Steven Moffat loves River Song, it's a possibility. Knowing that the meta-crisis counts as a full regeneration, it's an even stronger possibility. Again, it would be somewhat of an anticlimax to turn to the audience and say, "You should've watched that episode a series or so ago", but it's certainly more plausible than most ideas thrown around.