Julius Peppers has issued statements through his agent suggesting he doesn't want to be a Panther anymore. Citing a want to explore the free agent market, Peppers also apparently believes that the team has been holding him back.
The team doesn't have many options, and has already offered Peppers a huge contract he didn't sign. Now that the season's over, he's free to discuss options, and apparently Carolina isn't his preference. The team could still franchise tag Peppers, which would cost $17 million, and either trade him or attempt to make him play another year. This is a heavy amount of cap space (around 14% of the cap) to spend on a player that doesn't want to stay, and the risk of tagging Peppers while trying to hold him ransom for trade is weighty. So many things could go wrong in that situation, including a holdout, or Peppers signing the deal and playng for one year knowing Carolina can't continue to see the price raised.
I have no reason to believe that Peppers is being "held back". That's a dubious statement, given his success, and that the 4-3 defense is traditionally used as the best place one player can rush the passer every down. I doubt his fascination with the 3-4 will continue when it means he's dropping back on third downs to cover someone else's blitz (though this did happen, unfortunately, with Peppers here already).