Here is what Kazuto Yamaki (Sigma's CEO) had to say on the latest Foveon full-frame sensor development:
"Speaking of Sigma, a full-size Foveon sensor is under development. However, development has been difficult, and we have not succeeded in developing a full-size sensor at this time. President Yamaki explained, "I'm still researching pixel architecture with a small sensor." Although it was prototyped once, it seems that there is a technical problem and development is continuing again. However, if this is successful, it will be possible to start developing a full-size sensor as the next stage. There have been twists and turns, such as resetting development and changing partners, but President Yamaki still shows his intention to continue development. Depending on the status of this year's prototype, I would like to aim for next year's release." (source: Mynavi via Digicame-info).
Update - here is another Foveon quote from an interview with Phototrend:
"We are still in the technology development stage. We have not yet reached the final prototype stage for the full-frame sensor. We still make a smaller sensor, but with the same pixel size and architecture. We are now trying to use the latest wafer manufacturing techniques (an etched silicon plate from which the sensor is created, NLDR). But semiconductor companies are very busy. So we have to use current technologies to design our own 3-layer sensor. We are working hard with the fab (semiconductor factory) to improve our sensor with their technologies. During this stage, we inevitably encounter technical challenges. Some of them still need to be solved. Once this step is completed, we will have our new sensor. So it still takes some time."
