In an interlocutory appeal over an arbitration provision, the court to which the appeal is taken must only assure itself of the appellant's right to appeal and the fact that the court from which the appeal comes would have subject matter jurisdiction over a suit arising from the conflict between the parties.
As answering the question of whether a non-customer plaintiff is equitably estopped from avoiding a mandatory arbitration clause within a terms of service necessary for the use of the service is neither necessary for nor inextricably interwined with the question of whether the plaintiffs have standing to sue, the latter can't be answered under pendent jurisdiction on an interlocutory appeal as to whether the non-signatory is equitably bound to the agreement.
Since the plaintiff's are complaining of discrimination that keeps them from using the service, they are not equitably bound to agreement that they have neither embraced nor benefitted from.