There are other manufacturers waiting in the wings to produce a knobbed SDR radios. Besides ADAT there is this manufacturer who is on the right track.http://www.reuter-elektronik.de/index.html
Putting knobs on SDR radio is not hard if you know what you doing and have the incentive to do so. People like Flexradio dont want to do because of marketing reasons. If they really sat down and designed a front panel seriously
they would not have to chop and change the design every 6 months. A well designed front panel with knobs could be used across a whole platform of different radios. You could get a return on your investment over many radio models.
The Japanese manufacturers do this. If you study their circuit diagrams its the same electronics on different PCB's for different models. Its very rarely totally a 100% a new design.
I would not be giving up on knobbed radios yet. Its just that manufacturers just have a grip on or understanding of how to go about designing and utilizing the many available embedded industrial processors and systems that are readily available. I just bought a google nexus and I was thinking WOW what a fantastic front panel it would make. Its just so responsive and fast. If only I could just attach a USB cable and plug it into a K3 and P3. There we go knobbed SDR radio with touch screen and no PC!