Take it with a grain of salt because it's a generic teaser, but WWE's official DVD description for WrestleMania suggests that more legends could be returning at WrestleMania 29. Amazon has released the official description for the WrestleMania 29 DVD, which says that "several" legends will be returning and seperately mentions Triple H. This would suggest that either they consider two to three legends (Rock, Lesnar, Jericho) to be "several" or that more may be returning.
The DVD synopsis reads: "It only happens once a year, and in 2013, The Showcase of the Immortals comes to the greater New York City area for WrestleMania XXIX! From MetLife Stadium, the biggest stars in WWE and several returning Legends compete on sports entertainment's grandest stage. Last year, fans witnessed The Rock defeat John Cena in one of the most epic matches of all time.
"What legendary Superstars will thrill the WWE Universe at WrestleMania this year? Plus, John Cena, C.M. Punk, Big Show, Triple H, Sheamus, and several major Superstars strive to cement their legacies and create moments that will own a permanent place in WWE lore."