Whatever it is, it sounds pretty ridiculously epic. Even if the Doctor getting electrocuted over the phone is a little ridiculous taken out of context. On Doctor Who TV, somebody commented claiming the episode is titled "Prank Call of the Daleks".
Every year there are rumors and speculations that classic enemies will be returning--though granted, the Davros Hypothesis is a little more substantiated than others. I am constantly seeing theories that the Master will come back; I've seen suggestions that River Song was the Master, that Rory was the Master, and even that Peter Capaldi was going to be the Master.