Though this post started as a comment for Joey's post below (well worth a read, btw), I have been mildly heckled by the aformentioned contributor for being a compulsive commenter rather than poster, so here it is, posted independant of the comment box:
I think perhaps the answer in Iraq could be similar to the actions taken in Spain in response to regionalism. Differences in language and ethnicity have caused a similar sentiment amongst Spaniards as what is forming amongst Iraqis now that they have been presented with semi-representative government. The fall of Sadaam in Iraq can be compared with death of Francisco Franco in Spain and following plunge into democracy taken by King Juan Carlos. While Iraqis consider themselves Kurdish, Sunni, or Shia first and Iraqi second, Spaniards consider themselves Andalucian, Navarran, Basque, and Aragonese, etc. first.
What has occured in Spain to answer this dilemma is a system of government in which each region is semi-autonomous and elects its own empowered premier and assembly. The national government, meanwhile, is made up of a Parliament and Prime Minister. While the regional governments control the interests and laws of the region with a very firm grip on social agenda and regional economics, the national government sets national policy and addresses issues that effect Spain in its entirety, including issues of inter-regional relations, national security, foreign policy, and military strategy.
I have done a rather hackwork job of quickly describing this system. A much better analysis can be found here. While I am weary of leaving Iraq to its own devices, I think an extremely pragamatic solution to the political situation in Iraq would be to find a balance of national government with regional semi-autonomy. One would assume it would be significantly easier to first establish stable regional governments, and then allow those regions to then independantly run elections for the national assembly. Perhaps a bicameral body similar to the US Congress in which one house would contain one-third representation from each semi-autonomous region could be formed.
The timeline for an Iraqi government in which regional anxiety would be calmed by semi-autonomy of each ethnic group is far shorter than that of trying to form a national government from scratch. A similar plan to the Spanish transition seems the best solution to me.
I am curious to see if Biden's new report will contain a similar idea of regional independence in Iraq, but my fear is he will ignore the problems with full regional autonomy in Iraq and try to push a flawed agenda through the Foreign Relations commitee.