Back in 2011, Doctor Who and Sherlock both featured the main character apparently getting killed, leaving fans to figure out how he faked his death.
Right now, Doctor Who and Sherlock are both wrapping up 2015 with a threatening veiled undead woman.
Moreover, if you combine the adjective from the title of the upcoming Sherlock holiday special with the noun from the title of the 2012 Doctor Who holiday special, you get a 1967 Doctor Who story ….