Yeah there was a segment on NPR today.. it's getting hard to plot out who is where in the structure of things.
It's going to be truly epically nasty for a while. The State department announced there would be an expedited shipping of arms/drones to the Iraqi government
Though it's a rosy prediction, something like this could also be a unifying aspect. Unlike the first Awakening, which was sponsored by the Coalition forces, reapproachment afterwards was incredible strained largely because the Iraqi government under Maliki refused to include large numbers of the Awakening Militia or CLC (Concerned Local Citizen) groups into the Iraqi Army or Police respectively and because public works projects in the Anbar Province and other areas dried up when the Americans left. Naturally that resentment allowed Al Qaeda and its successors to be resurgent. (as well as capitalizing on the fact that the Coalition forces were probably more skilled in their operations then the Iraqi military)
Maybe now, confronting these problems without a large foreign military force also present, could be a unifying aspect to the Sunni-Shia groups within Iraq. If reports are true and Maliki is actually offering weapons to the Anbar tribes to help fight the ISIS and is calling upon Fallujah to help rise up and expel the the militants could possibly be used, further down the road, into providing more legitimacy and influence for the oft ignored Sunni factions in the government.
While it's a bit cliche, fighting a common opponent is obviously something that can unify disparate groups. With the examples cited earlier of India or South Africa, it's important to know that in the former, India does have a large Muslim minority (IIRC one of the biggest Muslim populations in the world) and even its non-Muslim segments are incredibly diverse ethnically and culturally and religiously and while it's not a first world country, it is 'relatively' stable and a democracy so 'tribalism' can be overcome. Same in South Africa, not everyone down there belonged to the same tribe, or were even just African or White. And while there are many problems, the country is relatively stable and a democracy. It can be argued that both have also had major events in their history which helped bond the disparate segments of the population together. Even if in both of those cases, it was an event that closely resembled a civil conflict or war.