Source: Wrestling Observer Newsletter
According to the Wrestling Observer several ideas for Undertaker’s role at Wrestlemania have been scrapped. He won’t be wrestling Wade Barrett, Sting has not signed a deal and Brock Lesnar was not given permission by the UFC to take part.
The only possibility left is some kind of match with Triple H, who is set to return in the coming weeks. As reported last month this idea has been on the cards, but seems to have been forgotten under the furor surrounding Sting.
As noted WWE also want to involve Shawn Michaels in some capacity, probably as a special guest referee.