Super interesting camera. I've always loved the Sigma foveon/quattro quality. I demo'd the DP2 Quattro for a week when it came out, and the image quality at low ISOs is beautiful. Build quality was also impressive, even if the ergonomics weren't the best. This looks like the same build style with a much better set of ergonomic choices, even if the weird angled base should have been flat. Seriously, I think they've designed these Quattro SDs and DPs to be visually strange in order to say, "hey, these aren't your average camera".
Sigma's approach here seems to be a way to take a step in the mirrorless direction, while taking advantage of an already built-out lens lineup. It's pretty much the only way that a smaller player like Sigma can release a system camera, since they probably need the volume from Canon and Nikon mount sales to produce any lenses at reasonable cost. They need to piggyback on the larger players' platforms in lens design.
By the same token, I wonder whether the release of the Sony and m4/3 30mm f1.4 means they may be testing the waters of a pure mirrorless mount system in the future. If these systems can provide enough lens volume, Sigma can start developing a smaller mirrorless system camera. Or maybe we'll see a Sigma Quattro "DP2s" with the 30mm f1.4 lens instead of the f2.8 version.
Unfortunately, Sigma still hasn't addressed what I think is the achilles' heel of these cameras--the horrendous SPP software that is basically required to get the best out of the RAW files. I could totally get on board with a specialty camera like the DPs or even a system like the SD, but SPP introduces another layer into the post-processing pipeline that leaves a sour taste in my mouth. I just want to import my files into Lightroom and edit, not have to import/export through SPP to Lightroom, creating and managing multiple files along the way. If anyone has a simple workflow for these Sigma files, I'd definitely take a harder look at a Sigma camera.