Sallow
The Big Bad Wolf.
He probably would try to establish some sort of Iran-based government. Muqtada has, in the past, rejected Iran, but praised the Velayat-e faqhih. I believe he viewed the Iranian government as corrupt and an improper representation of Islam (or maybe it was bad blood from the decade-long war). But, since he spent nearly half a decade living in Iran, he seems to have changed his mind.
Still, the Kurds would not go for that and Muqtada doesn't have enough national support. His primary base is with the poor, particularly in Sadr City in Baghdad. He's gained a lot of power in the south, but the ISCI is still bigger and more powerful than the Sadrists.
It won't work. Iraqis still have a bad taste in their mouths over the Iran/Iraq war. There may be a treaty of some sort but tribalism will quickly kick in.
They have a common "enemy" now. Remove it and the old hurts will kick in.