This week's Time Out is tube themed and has an interview with Tim O'Toole, the man in charge at London Underground. He says the usual stuff about Crossrail, Thameslink and other things before dropping this bombshell:
We've also got plans to extend the Bakerloo south.This is news to me (though apparently not to Wikipedia, where an anonymous user claims it's part of the Mayor's "South London Tube Plan", whatever that is). The TfL Transport 2025 document has no mention of a southern extension. The only thing I can find that backs it up is this evergreen news story, which is indistinguishable from Ken being polite to a campaign group so they'll go away.