There has been talk of doing Ryback vs. The Undertaker at WrestleMania 29 with a Streak vs. Streak build. We've noted before that the CM Punk and Ryback interactions are just teasers. Apparently they're not looking to do anything solid between Punk and Ryback until November or December.
Speaking of The Undertaker, with recent WrestleMania discussions happening, there are some people speculating that Taker may not even perform at WrestleMania 29, meaning last year may have been his last WrestleMania match. While nothing is 100% yet, the feeling among most is that he will return.