It's simple...a digital ND filter built into the camera or rather, the digital equivalent.....ISO expansion. The 'true' ISO is not really lower...same as Canon DSLR's now with their ISO 50 setting. Only multiply that times four...y'dig?
The Canon DSLRs with their ISO 50 setting are
plainly overexposing the shot; the same with ISO 100 on some Nikons. That is not what you are looking for.
I guess it could be done, but at a very high price. The sensels would have to be read several times during the exposure and those, which reached a certain saturation level, would have to be reset (and that fact would have to be recorded). However, the electronics on the sensor chip would have to be much more complex than it is now: resetting individual sensels is not in the cards by the row or column oriented processes.
This way practically unlimited exposure could be realized. Dynamic range 15 EV, 20 EV, 30 EV - how about that?