Brian argues, based on Justice Kagan's excellent dissent (which is quite good and worth a read), that Genesis won't have much effect. My view is different.
Justice Kagan effectively skewers the majority opinion for its failure to address the crucial threshold premise that underlies its decision: i.e., that an unaccepted Rule 68 offer moots an individual claim. And Justice Kagan debunks that premise itself.
But her arguments, while persuasive, do not govern the circuits that have already decided (wrongly) that a Rule 68 offer does moot the individual plaintiff's claim. As the majority notes (at note 4), this group includes at least the Third Circuit, from which this case arose, and the Seventh Circuit. The majority also notes that at least two other circuits, the Second and the Sixth, permit a district court to enter judgment on an unaccepted Rule 68 offer, thus effectively forcing the plaintiff to accept it. Until these courts of appeals reverse themselves en banc or the Supreme Court overrules them, collective actions in Delaware, Pennsylvania, New Jersey, New York, Connecticut, Vermont, Ohio, Michigan, Kentucky, Tennessee, Illinois, Indiana, and Wisconsin are subject to being undercut by Rule 68 offers that "pick off" the named plaintiff. Class action plaintiffs could be subject to this treatment as well, despite the majority's general statement that the two contexts are different. I understand why it's a powerful rhetorical device for Justice Kagan to argue that today's decision is meaningless, and how that argument supports the dissenters' broader point that the majority once again (following on the heels of the Comcast decision) reaches out to decide the wrong question. But the view that this decision is, in Justice Kagan's words, "the most one-off of one-offs" is not correct.
Brian and I do agree on this: the dissent will be a useful persuasive tool for plaintiffs in jurisdictions where the law is unsettled. Let's hope the others eventually come around to Justice Kagan's view as well, so that the Genesis case doesn't matter for too long.