Chris, I too have requested this feature then for the BMCC - years ago.
But I think there is a good reason why this won't be implemented with the current hardware and firmware. With longer exposures beyond 360° you quickly start to get into all kinds of sensor noise issues where the implemented calibration won't work as expected anymore. And stuck or hot pixels and so on.
Like Anatoly wrote with averaging frames and getting vertical stripes this would also show up with those much longer exposure modes. Blackmagic would need a different approach for sensor calibration and in-camera noise reduction which is likely not happening anytime soon or maybe even impossible.
So your best bet would do what Anatoly did. Average out and fuse several frames into one. And you would need somehow to create a reference frame for subtraction to cancel the vertical stripes out in post.
https://wiki.apertus.org/index.php/Black_Calibrationhttps://wiki.apertus.org/index.php/Pattern_Noise