Why no digital ISO50 ?

Jack Hogan wrote:

I wonder if this will change with the next generation of sensors, with usable PDRs exceeding 12 stops. We are already starting to see ways to change the Full Well Count dynamically (as in Aptina's latest designs) - and I wonder whether DSLR manufacturers couldn't design a new semi-transparent-mirror to optionally leave down during capture, therefore acting like a 4+ stop built-in ND filter.