A unity government is very unlikely now. The gulf between them is wide right now.
"Vali Reza Nasr" is an United States/American academic and author specializing in the Middle East and the Islamic world. He is currently Dean of the Johns Hopkins School of Advanced International Studies in Washington, D.C. and a Senior Fellow in foreign policy at Brookings Institution.More Vali Nasr on Wikipedia.
The key issue will be what kind of power the Sunnis get from these numbers when it comes to negotiations about the government. What kind of cabinet posts will they get? How will resources be distributed? What kind of representation will they have in patronage and government?
What you have in Iraq is not just a society coming apart like Yugoslavia or Congo. What is at stake is not just Iraq's stability but the balance of power in the region.
For the first time, talking to the US has the endorsement of a very powerful conservative faction in Iran.