The new Arri cameras do some interesting tricks to get High(er) Dynamic Range video:
Lots of secret sauce in the sensor, most of it we cannot talk about.
One thing we can talk about is the Dual Gain Architecture. We are taking the signal from each pixel, and splitting it into two different pathways. One with high, one with low gain. So out of 32 signal paths from the sensor to the A/D converters now we have made 64. Each goes into a 14 bit A/D converter, and then the high gain and the low gain 14 bit images are being re-combined in the camera electronics into a 16 bit image with meaningful brightness data in all 165 bits. HDR.
Yes, this is what I was thinking. What we are talking about is purely digital data. If the raw data could be duplicated or triplicated and fed into different processing streams, you would not need to have multiple exposures for each of the HDR passes.