There are rumors of him retiring as well as Shawn Michael retiring due to injuries(knee injuries, hip injuries, back injuries). There are a lot feeling that Jeff Hardy will be leaving WWE in two or three weeks but, the biggest feeling is that these three superstars will be appearing at Wrestlemania XXVI.
The Undertaker has won everymatch he has been in at Wrestlemania and some of the wrestlers that are on the roster right now have been defeated by him in that ring, including Mark Henry, Triple H, Randy Orton, Batista, Edge, and Shawn Michaels.
But there are some superstars that are on top right now who he hasn't faced yet:
For example John Cena, Rey Mysterio, MVP, Big Show, and others.
Here is a list of the five wrestlers I think that would be great to watch feuding with taker at the greatest stage of all, Wrestlemania.