I stopped by the Sigma table at the Sneak Peak press event at PMA. I was told by a Sigma rep that the DP2 should be shipping sometime in March. He thought it would take a different lens hood from the DP1, but will be able to use the same close-up lens.
I asked if there were any plans to put the DP2's faster processor into the DP1. He said he didn't know. It would depend on whether they could just replace the processor versus having to redesign the camera.
They do plan to sell both. The DP2 doesn't replace the DP1.