While Take-Two filed last week to renew the trademark for the game, we still have heard nothing about a possible Bully sequel. Of course if they are going to do a sequel, renewing the trademark would be a good move.
If a sequel were in development, many sources seem to believe that it would be in development at Rockstar Vancouver who is the same studio that did the first Bully game. At this point if it is in development sources also believe that it would be a next-gen title, but that is of course open to debate. If it is in development, they have done a good job in hiding it, because everyone time someone asks about it no one seems to know anything about it.