When you pull a sensor down from a very high native ISO of 3200 for example to 400 it is true that your lower ISOs compromise the image. I.e. dodgy highlights, banding, etc. We see this on the low light kings FS100, 1D C. This is a problem waiting for a fix. Of course what you describe with F32, high shutter speed, stack of NDs is not the answer and you're right to point the issue out. This sensor probably isn't a general purpose one!
Red Dragon is rated at 2500 native I think.
I think some stuff is already looking too plastic and too clean. I actually WANT a bit of grain. But there's no denying how excited I am about the low light possibilities.