The political future of Iraq is uncertain because of the intensified domestic splits between its constituent Shiite, Sunni, and Kurdish communities which were exacerbated by Daesh over the past couple of years. Post-2003 Iraq has been continually plagued by communal violence, but never before had each of its three communities been so divided from one another.
Up until this point, none of them were able to stake a plausible claim to quasi-independence, except of course the Kurds, but even so, Erbil would have been unlikely to succeed with this so long as the Iraqi Army projected an image of strength. Nevertheless, that's exactly what it was -- an image -- since it's well-known how quickly they retreated in the face of Daesh's advances in summer 2014. The present situation of dramatic domestic divisions within Iraq are most directly attributed to that moment, as the presumably "unified" state thenceforth ceased to exist once Baghdad's authority was essentially restricted to the capital, and even there, it wasn't functionally present in all neighborhoods.
The ongoing liberation campaign in Mosul is progressing at a snail's pace, and that's partially attributable to both the dangerous mistrust between all "allied" factions and the US' efforts to maximize the latter in order to further divide and rule over its former de-facto military colony of Iraq. Moreover, the involvement of two other foreign powers aside from the US -- Turkey and Iran -- makes Iraq a cauldron of proxy conflict on par with Syria and Afghanistan.
Generally speaking, Turkey supports the Kurdish Regional Government (KRG) due to the intimate pro-Ankara ties that its leader Masoud Barzani has cultivated for years, Iran supports the Shiite militias, and the US stands behind the Iraqi Army and select Sunni tribesmen. Although there have been reports of tension between the Kurds and Shiites (and more broadly, one could generalize as being between Turkey and Iran via their Iraqi proxies), the crux of potential civil conflict in Iraq is between the Sunnis and each of these two groups.
Additionally, Baghdad -- no matter which ethno-religious faction is controlling it at any given time -- is for the most part consistently reluctant to further devolve the state, meaning that it will resist Identity Federalism in a post-Daesh political environment, though it's uncertain if it would go as far as commencing a civil war over this issue. This brings the analysis around to discussing the prospects for a renewed period of domestic conflict after Daesh is cleansed from Iraq. Neither Turkey nor Iran wants to have their shared neighbor embroiled in a prolonged and unresolvable war, though both of course have their own interests to protect within their mutually adjacent state.
However, given that Tehran and Ankara are enjoying a renaissance of relations with one another ever since the failure of last summer's pro-American coup against Erdogan, it's unlikely that they'll take any dangerous and unilateral moves which could be interpreted by their counterpart as potentially sparking a civil war. Therefore, it's much more likely that both Mideast Great Powers will likely advocate in favor of expanded federalism in Iraq and the legal establishment of three de-facto independent statelets centered on the country's three constituent identities.
To be fair, the pro-American Sunni minority in the country is also somewhat in favor of this, and had been previously agitating for it. The problem -- as they perceive it -- is that the prospective Kurdish and Shiite regions of an Identity Federalized Iraq contain the majority of the country's oil and most of its economic activity, meaning that the Sunni portion of this political arrangement would likely be the poorest and least developed, which could possibly provide fertile ground for the cultivation of radical ideologies and the subtle prolongation of Daesh sympathies.
Even if the Sunni part of the country were to somehow reach a deal for resource and revenue sharing with the other two portions -- which is very unlikely -- there's no guarantee that this could serve as a panacea for its economic and ideological ailments. Therefore, no matter the domestic constitution of post-Daesh Iraq -- whether federal or otherwise -- it's foreseen that the Sunni-majority parts will remain the most conflict-prone and susceptible to outside ideological influence and provocations, ergo why the US appears to favor it.
Washington understands that this community can provide a reliable platform for dividing and ruling the interconnected "Syraq" battlespace, and while the Kurds could also function in a similar strategic fashion -- and actually do to a large extent, given their close ties with the US and 'Israel' -- there's a strong chance that the Tripartite 'Concert of Great Powers' between Russia, Iran, and Turkey could succeed in neutralizing or at the very least mitigating this geostrategic threat. However, it's less likely that they could do this when it comes to the transnational and ultra-'traditionalist' Sunni communities straddling the rural areas of "Syraq", as the optics involved would be extremely negative and could inadvertently provoke wider regional tensions, to say nothing of dividing the incipient Tripartite by isolating Sunni-majority and Muslim Brotherhood-influenced Turkey.
Looking forward, the on-the-ground division of forces in post-Daesh Iraq, dependent and influenced to a large degree by the ongoing liberation campaign in Mosul, will provide the firmest indication of which political direction Iraq is headed in. The potential for identity conflict in the immediate aftermath or just prior to the conclusion of this war is very high, and the US and its Gulf allies might seek to provoke this scenario in order to more easily divide and rule "Syraq" and create asymmetrical challenges for Turkey and Iran.
The ideal eventuality would be if Iraq were to somehow return to its tense but "unified" former nature, but this is all but impossible, meaning that it's much more likely that Identity Federalism will be implemented to a large degree sometime in the future. This brings with it a host of problems, namely over the territorial reorganization of the country, particularly as it relates to Kurdish claims over Kirkuk. Other expected problems could be over revenue sharing, the organization of each statelet's own military forces, the division of Baghdad, and the authority that the central government and its organs (military, tax, diplomatic, etc.) will hold over each of the three entities.