hmmm ... al-Sadr has been since the invasion a behind the scenes political leader forming a significant political block representing Shia interests.
Our differing perceptions may not go much beyond semantics, rporter. I see as you do his actions to form "a broad coalition spanning religious sects", which of course in Iraq translates into a "broad coalition spanning political parties". I see his primary interest being, like that of his mentor Ali al Sistani, the furtherance of Islam, and his secondary interest, also like that of his mentor, the preservation of Iraq.
To my mind, neither of these concerns is in and of itself political. I agree too that he could very easily be the "glue" to hold together the fragmented Iraqi society. But he does not need to be a political leader to accomplish that.
In fact, it may be easier, and better, for Iraq to be united behind a religious leader rather than a political one. In fact, it may be a stumbling block for us Americans to assume otherwise. It may be better for all concerned for us to accept the possibility that Iraq would prosper more if it were released from the requirement of secularism and allowed to emerge first as a theocracy and then perhaps evolve into a secular Parliamentarian Democracy.