In a recent interview, Sigma's CEO Kazuto Yamaki mentioned that they are planning to use the new Foveon X3 Quattro Direct sensor from the DP2 Quattro compact camera in a future Sigma DSLR body:
First, we started with the sensor development. We had already been discussing what kind of sensor we make with the Foveon, Inc. and we as SIGMA wanted to improve image quality (resolution) by increasing the number of pixels. The Quattro image sensor was born to deal with the increased data. As the first camera to have the new sensor, we chose the dp because of the shockless body and the dedicated lens optimized for the ultra high-resolution capturing. Of course, we're planning to use the sensor for the SLR SD body.
Here is more info on the new Foveon “Quattro” Direct Image sensor (from Sigma's press release):
Foveon “Quattro” Direct Image sensor with a Bayer equivalent of a 39 MP conventional sensor in resolution testing. The next generation sensor builds on the distinctive properties of X3 technology which uniquely records red, green, and blue wavelengths at each pixel location within three layers.
The Quattro sensor is a three-layered, panchromatic silicon chip whose green-sensitive middle and red-sensitive bottom layers each have 4.9 MP and record only color/chrominance information. The top blue layer captures chrominance and resolution/luminance information with 19.6 MP, resulting in greater detail capture and resolution capabilities that are higher than the Merrill DP camera line. The Quattro sensor’s architecture also contributes to true color rendition, more detail capture, and faster image processing, all of which delivers even more realistic images.
The current Sigma SD1 DSLR camera was introduced in 2012.