I'd hesitate to call Ollivant's analysis "optimistic". He foresees utter Sunni defeat and disenfranchisement, and decades of terrorist attacks to come from that.

The only problem with this excellent analysis is that it really doesn't take into account ISIS' "strategic depth" in Syria, and the lack of a ground force that can destroy ISIS in that area. ISIS may lose northern and western Iraq eventually, but one cannot imagine the war ending without a similar endgame in Syria.