Who knows?
What I'd hope for, if assembling the team, was a prototypically sized sg with athleticism and a great outside shot, who could hunker down and play defense as well. Being a solid ballhandler wouldn't hurt, either. For a center, simply being a good rebounder and rim protector would be great, maybe with an offensive game at Gortat's level--someone who needn't be a focal point offensively but who could still score when necessary and keep defenses honest.
If the Celtics could manage to find someone who is more of a game changer than Jeff Green, that's great, but he can be a solid third option and is capable on both ends of the court. What he can do would be valuable to nearly any good team out there without superstar sfs (or Nic Batum), and I don't think he would be a weak link to a solid team.