I doubt Shaq would accept a minimum contract, and I doubt he'd accept 10 to 15 minutes per game. Those are the only circumstances under which I'd want him on the Celtics.
I think Shaq still has quite a bit left in the tank, honestly. He can score in the post, he can rebound, he can defend the low post. However, he doesn't really add a ton to our team. He's a slower version of Perk at this point, with a better offensive game. For our backup center, I'd prefer somebody with more mobility, who can help us against more athletic teams.
Shaq is still going to be best on a team that wants to run an inside outside game. There, he can still be effective. It wouldn't shock me to see him sign with a team like Miami or Chicago, depending upon whatever other stars they sign. However, I can't see him here.