Verified answer

Well, yes and no. Let me explain:

JD will only be in the first 6 episodes the season.

HOWEVER, Zach Braff is also working behind the scenes ALL season as an Executive Producer.

Yes, everyone is returning, including Dr. Kelso, and Nurse Shirley, played by Aloma Wright, who played Nurse Roberts, who was killed in season 6, when they thought the show was ending. Bill Miller promised to write another character for her when the show continued. Dr. Kelso, who is not the Chief of Medicine anymore, will become a confidant of Dr. Cox, who is the new Chief.

yes, he will only be in like 5 episodes of the entire season

He will have small bit parts, but no carla this season :(