More important is the discussion of "Whereto from here?"
Quite frankly, I think the only solution is a loose federation of affiliated states as neither the Shia nor Kurd trusts the Sunnis to be part of a ruling government with jurisdiction over their territory....and based on their behaviour under the previous regime in particular, I find it hard to blame them. The difficult part will be how to arm each of these federated states. My own opinion is that in the constitution there needs to be a clear statement of only ONE central army for as soon as you get regional armies, or even militias, you are very quickly going to see outside interests leap in to cause great difficulty. The Iranians have already started this by arming the Mehdi Army. The Americans have been arming the Kurds for years (with good reason) which leaves the Sunnis who would likely be befriended by whomever they offer oil rights to (Russian, China, France....maybe the USA).