Smart, KO, Sully and Young are the four current C's with future AS potential. (Bradley might slip in at some point in his career, too.) I think two Celtics make it next year, with at least one of those slipping in as an injury replacement. I think Young is at least another year away, however.
My best guess is either KO or Sully and another player not yet on the team slip in next year.
Three C's make it the year after that.