One big obstacle to implementing this plan is the mindset of the Bush White House. Administration officials would have to accept a reality they never quite acknowledged before the war: that a democratic and truly sovereign Iraq may do things the United States doesn't like. In particular, they would have to let go of a primary, if rarely articulated, motivation for the war: to use Iraq as a platform from which to project American military power.
From the beginning, this goal was essentially incompatible with the professed goal of democratizing Iraq. A democratic and sovereign Iraq was never likely to let American troops use its soil to intimidate its various neighbors. How President Bush and his advisers mentally reconciled the idealistic and realpolitik rationales for this war is a question for future psycho-historians to answer. In any event, the contradiction is now manifest, and we don't even have the luxury of choosing between the two scenarios—between a democratic but unwieldy Iraq and a non-democratic but strategically valuable Iraq. Only a stable Iraq would be useful as a strategic platform, and an Iraq being used as a strategic platform is unlikely ever to be stable.
Even once you abandon the realpolitik and try to salvage the idealism, things will remain iffy. There is of course the chance that demagogues could hijack a democracy, ushering in authoritarianism and/or theocracy. And there is the chance of a breakup into completely separate states—possibly, if we're really lucky, three or four fairly stable democracies, but more likely some combination of democracies and authoritarian states, with the risk of conflict among them (especially if ethnic minorities are persecuted).
But if democracy survived and flourished in the predominantly Shiite region, we'd at least have accomplished the laudable part of the neoconservative agenda, "planting the seed" of democracy in the Arab world—thus partly compensating for all the aspiring terrorists this war has created there and in the larger Muslim world. (And if a sovereign Kurdish state emerged, the less laudable part of that agenda—an American military presence somewhere within Iraq's current borders—might be revived. For better or worse, the administration's aims would have been miraculously salvaged by the collapse of its game plan.)
In short: This plan is a roll of the dice. But what alternative isn't? The idea behind this war was that you have to break eggs to make an omelet. Anyone who thought you could break the eggs gracefully, or that the omelet was guaranteed to materialize, was confused from the beginning. I won't mention any names.