There's no way KG would ever come off the bench. You would have to chain him to it. Besides, the Garden wouldn't be the same without The Big Ticket hopping around, screaming and beating his chest at the crowd right before tip-off. It just wouldn't be right. He just needs a few less minutes.
I don't see why Ray Allen can't still start. He doesn't seem to noticeably tire throughout a game, like Paul and KG. And he does more running around than anyone. Dude is ageless. He's like the Ichiro of basketball. I wouldn't be surprised if Ray Allen were a robot from another planet and was 9000 years old and once trained under Yoda.
However, I can totally see Jeff Green starting. Doc can incorporate him more into the offense, and he can play more minutes with Rondo, Ray, and KG. I can picture Pierce, being the awesome team captain that he is, not having much of a problem assuming the Manu Ginobili role. He can solve the bench's scoring problem, and he'll still have his legs when he needs to throw daggers in crunch time.