I think they have thought about it. Actually, I should rephrase that a bit. They cannot agree on anything, so it's almost as if they haven't thought about it, because no plan has materialized with regard to how to really govern these areas as they're liberated from Daesh.
Even within the Sunni community, I heard former governor Atheel al-Nujaifi, who was governor of Nineveh, saying that it should form a region. The current governor of Nineveh didn't even attend the talk, is dead set against that kind of proposal, and is accused of being financed from Baghdad. Then you have others who say that they should do something else.
We haven't been able to arrive at anything even approaching sufficient consensus to move forward.