I think this is what will happen: Cena will rather sooner then later take the title off Punk, but only for a short time, after which Ryback will take the title of Cena.
Ryback then reigning over the WWE-roster for a while destroying everything in his path, always demanding 'feed me more', going completely frenzy, and after destroying several Top Stars going Heel by crushing everything left and right. Announcers, wrestlers, fans, divas. Always demanding more and more.
After one of those frenzies doing a promo he stands in the ring with the title, yelling: 'Feed me [Lights out, Gong, Gong, Gong]'. Taker in the ring, challenging Ryback for a Streak vs Title match at WM. Taker wins title, then resigns, title vacant, then goes back to punk who will win it in a contenders tournament. I know, not very realistic, but it would be a storyline i would like.