Last night during the segment with Bray Wyatt you could see (barely) the words "The Man Comes Around" on the big screen. That is the title of a Johnny Cash song so this could mean that we'll be seeing The Undertaker come out to this song or at least the first part of his entrance could be this song and then it would lead to his regular theme playing. Taker is a big fan of Johnny Cash. The song was one of Cash's last songs written before his death and it is sung and spoken with several Biblical references from the Book of Revelation.
WWE used Cash's "Ain't No Grave" at WrestleMania 27. You can hear the song below.