If you see that much difference in the sensitivity then it is almost certainly measured in a different way, probably deliberately incompatible with the other specs, or there is some reason that you wouldn't use it at the same ISO.
I think you really need to look at the specs Nigel. Sensitivity isn't just down to size but makeup and whether or not groups of pixels are used to collect light eg. many of the better sensors are actually around 9m but only using 4mp for the image which suggests there's a lot of other pixels in there - grouping maybe? I wouldn't know. I believe the 334 is quite large anyway isn't it? - 1/1.8.
One of the reasons: The high resolution DSLR sensors are often fitted with strong anti-aliasing filters to avoid moiré and false colours. At pixel level they are often very blurry compared to an IMX 323, but it doesn't matter because they are mainly used for photos in good lighting and have more than enough resolution. They also have to work well with long exposures, maybe 1 hour, and still produce accurate colours and low noise, surveillance sensors only need to work down to 1/30th second for 30fps, they are never used for photos! There are probably quite a few design differences, a surveillance camera doesn't need accurate colours or shading or particularly low noise, it just needs to capture detail.
Not saying that doesn't hold true fro most cameras, but have you seen cameras such as the GX4 / 5 and Sony's A7iiS (although I believe the sensor maybe in house for that one?)
Deliberately chose this vid as it features driving - some of the scene setting clips / internal car clips aren't sharp - some deliberately blurred and others where the autofocus and the Sigma lens maybe aren't working as well together as they should. However, some of the out of the screen clips are excellent:
I suggest looking at 18 secs, 45 secs, 58 secs, 1 min 40 secs for unlit rear view (poorer quality):
First time I've ever been able to retreive a plate from a night time video where vehicles are moving and it's on Youtube at 1080P:
Possibly although maybe it could be designed out with a heatsink such as what Mobius did with the M1.
As for some other comments above - didn't want to turn this into a huge post of quotes, personally, I wouldn't want a B&W image at night and with regards to cost, for sure what we're talking about here is not going to be a camera such as the Wr1 or A119Pro in price, at least if we're talking potential DSLR sensors. A 334 sensor *might* be more obtainable, although even then, I doubt it would be cheap enough for a sub $100 cam . Any camera using such high end processors is probably going to need to be in the $200-300 range to be viable, and that's assuming even if that's possible, or in other words, what we're talking about is something that could probably only ever be high end enthusiast, at least in the foreseeable future.
