Is this the Active Pixel Colour Sampling sensor that obtains colour data for every pixel. The IMX189 CMOS single layer sensor is rumoured to be the first to use this approach.
Here is a diagram of how it works:
http://www.sonyalpharumors.com/sr4-d...mpling-sensor/
I have not seen any detail on how long bulb exposures would work, unless perhaps you have to set the exposure on the camera controls and it then moves the filter matrix to build the sub. So a 300 sec sub would be exposed for 3 x 300 seconds to build a RGB 300 second sub which would take at least 900 seconds to generate in theory.