There is not much beyond what they have already that is still a Sunni region. I think and have heard they have embedded sleepers in Baghdad. Kind of obvious with the rash of prominent bombings there. generally the Tigris river divides the Sunni to the west and the Shia on the east bank. I do think ISIS would like to get into Baghdad. It would be a hell of a recruitment on the media for them. There are a number of Sunni tribes and some Sunni militias aligned with ISIS. I doubt it will remain so, but just using them to gain ground on the Shia. They may be more welcome than we would like to think in Western Sunni districts of Baghdad.
Whatever ISIS was before, it will become bigger, and soon — but so will the battlefield, and the financing is already shrinking. When there is no more booty in the form of weapons, military vehicles, and ammo, they’ll be reduced to fighting mano a mano with the many other jihadist and other armed groups. Destruction of the Arab states remains the longstanding goal of Iran. Their loss of their ally Morsi in Egypt turned their plans into the ditch, but they are spread across northern Africa, into Arabia, and have ties both in Central Asia and Latin America.