Chang's arc was hinted at in the very last shots of the third season finale. Apparently we haven't heard the last of Central College.
I *did* like this week's episode. Possibly my favorite of the season. If it is, I wish I had high hopes for the final four epsiodes.
Incidentally, this week they didn't really conclusively say what happened to Pierce. Was he not in the "present" scenes because they filmed them after he was booted from the show? He wasn't in the publicity photo of the cast with their puppets either, though arguably he wasn't meant to be shooting that day anyway since he'd gone crazy, or something.. Still, the rest of the cast looked like they were having a great time doing this one, and it was awesome seeing them enjoy it with all this news of drama behind the scenes leaking out all the time.