In Phillips v. Ford (consolidated with Boxdorfer v. DaimlerChrysler) (pdf), the Seventh Circuit issued a ruling about the Class Action Fairness Act that should come as no surprise to anyone who has been following the Seventh Circuit's other CAFA rulings.
While the Seventh Circuit has issued other rulings denying a defendant's attempt to remove pre-CAFA state-court class actions to federal court based on events that happened in the case after CAFA was enacted, there has not been a specific ruling on the question of whether adding new class representatives amounted to the "commencement" of a new case under CAFA.
After Phillips, the answer is no. In Phillips, the Seventh Circuit ruled that amending a state-court class action to add or substitute new plaintiffs does not "commence" a new case under CAFA. If the state-court class action was filed before CAFA was enacted, the addition of the new plaintiffs will not trigger a CAFA-sanctioned removal to federal court.