It's not going to happen, at least not in any permanent kind of sense. Al-Maliki depends on the militias to support his coalition. His security forces are thoroughly infiltrated by the militias. If he goes against them the best he can hope for is that he'll just get pushed out of office...but it's just as likely he'd end up dead.

Plus, all of this assumes that he even wants to rein the militias in. And why should he as long as he's got the U.S. military there to protect him from the consequences of Sunni retaliation?