I know with the lack of any NBA news during this mundane off-season, the thought or sight of a situation like this, people dive in head first into discussion with out thinking thoroughly. Stephen Jackson is definitely one of the better players in the league, but lets look at his game overall. Jax is a ball-stopper on offense. Celtics already have one is name is Paul Pierce. Now if Jax were to somehow miraculously arrive in Boston, and was willing to play a role-players role well then thats a different story, but since he's been in Oakland, offensively he takes to many dribbles and takes to long to make a move or take a shot.
GSW runs a more open gym type of offense, with little to no structure, where as Phx runs (or ran) a run-and-gun style with a rhythm and some structure, so S. Jackson was GSW option if they couldn't get any thing in transition or off a fast break, and with that he would never pass the ball while in a half-court setting.
I live in Indiana, and when he was playing for the Pacers he did the same thing, not as often as he does now but enough to where he didn't have the best reputation on the court as well as off the court from the fans perspectives.
So all im tryna say is, he wouldnt fit into what the celtics do b/c we already have PP.