The Kharijites were a faction inside of early Islam that heavily invested in the concept of takfir (excommunication) and had other differences with both Sunni and Shia to the point where they were themselves considered no longer muslim and ended up mostly being killed off. ISIS, by its extreme actions, seems to have some significant points of congruence with the Kharijites. Foremost among them seems to be this shared belief in takfirism. It is not a perfect fit, ISIS’ ideology includes the idea that the Caliph should be a Quryash tribe member, something the ancient Kharijites rejected at the time.
Not having a dividing line between those who want to kill us in the name of Islam and those who we can live with underneath the big tent of american tolerance makes war difficult. Is neo-kharjitism a dividing criteria that would work both within Islam and without? It’s something to keep an eye on and a great tool if it can be relied on.