Word on the street is....
The WWE has been in talks with the Undertaker and Brock to do some wrestlemania PPV. When Brock walked by, he looked at the Undertaker and said 'wanna do it?'. The Undertaker, was kind of shocked and then asked the same question back. If you watch again, you'll see he was asking the question with a friendly tone, not a threatening one. He covered up well afterward, because he was taken be surprise and he's not supposed to talk about the WWE thing.
I don't know about you guys, but I have no interest in the WWE, and I think it'd be pretty weak for Brock to go back and forth between the WWE and the UFC.