Seems to be ineed their plan.
And not only according to the BBC the Iraqi army fails.

I think Option 1 is the most likely, because I can not see a basis upon which a strongman could erect his rule. The tribal militias seem to work however. Note how Al Sadr already demands the creation of sectarian militias in one of the articles. The split would probably be in between Kurdistan (which is already only loosely connected to Baghdad), Shiites and Sunnis. I dont know too much, about the Iraqi population, though. Do the Sunni and Shiite groups live in the same areas or is there a clearly Sunni and a clearly Shia part of Iraq?