Christian has posted a detailed status update to the osmocom-sdr mailing list, describing his progress with enhancing the sample rate from 500 kS/s to 4 MS/s (at 14 bits ADC). Also, some impedance mismatch between tuner and ADC was fixed.
The benefits of this are not only available to the users/customers of the next generation hardware, but there will be a stacking board to upgrade the existing OsmoSDR units.
The full details can be read in his mailing list post
At this point there is no ETA yet when the new design will be available,