Along the lines 10 years ago of the argument of some over what year was the new millennium, 2000 or 2001, what is the wrestling philosophy over what year a decade ends, the 9 year or the 0 year? If it is the 0 year, an interesting scenario could develop in the year 2011. Both Undertaker and Sting won their first world championship in 1990, which could be determined to have been the conclusion of a decade. That would mean that there could be a competition between the 2 to become only the second wrestler (Lou Thesz being the other) to win a world championship in 4 separate decades. If it is marketable, I'm sure the promoters will consider the 0 to end the decade.
Here are some more thoughts from a demented mind in Central Florida: I hate to rain on your parade, because it's an interesting point you pose. However, last I checked, 'Taker didn't win a world title until winning the WWF World Title from Hulk Hogan at Survivor Series in 1991. Are you counting his USWA Unified World Heavyweight Championship reign? (I'm ass/u/m(e)-ing not, since that happened in '89, and you referred to his first world championship as being in '90.)
Sting, however, might just qualify. But I don't know if he has enough gas left in the tank to pull it off.
Why yes, I am both a musician and a lawyer. Thanks for asking. :)