Do you really think Pentax could come in fighting Nikon and Canon, and also Sony (losing money there I suppose) with a 24*36 system, and I repeat system?
Where is a large part of the market going? Do Pentax have something there?
They know they can't compete in the 35mm FF pro segment, in fact they developed something different, the 645D. That is pro.
Being the sensors what they are becoming (more than enough for the pros), Canon and Nikon go on with the FF cameras JUST because many pros have huge investments in lenses, big and dear lenses. Look, pros don't pixel-peep. If the sensor gives what's enough for print, and that's happening, why big.
Yup, ok, a bit bold but that's my opinion.