Sistanis previous appearances as a "moderate secular" regarding the Govt-to-be was just Taqqiya type posturing so as to allow the shia in Iraq to consolidate their power and logistics.....Bremer and Senor et all got chumped and got out while the gittin' was good.
Sistani is not stupid and knows exactly that now the likelihood of a premature withdrawal by the US has risen dramatically. There will be no one standing between the Sunni Insurgents and the Shias, and so he wants to ensure that the only force able to defend Shias (the Mahdi "Army"), with the same dirty methods as the Insurgents, is kept within the greater Shia coalition.