Thing is, unless the Celtics are going all-in to try and keep Rondo, it doesn't make sense to target any of the centers mentioned who are already 27 / 28 years old. They'll be on the wrong side of 30 by the time the Celtics are read to be really competitive.
Personally, I think the best plan would be to find a veteran stop-gap solution at center for a year or two, ideally one who comes cheap. This could be Asik, provided no significant assets need to be given up to acquire him, or it could be somebody like Emeka Okafor.
Then, the team can draft a project big like Jusuf Nurkic or Clint Capela, or wait for a future draft or free agency opportunity to find a long term solution at center.