Thank you fikkser, interesting thoughts.
One can still argue re. diffraction, that it limits the interest of higher resolution, if it has no worse consequences. For optic resolution, i guess it could be identical.
I still would be very interested to see Nikon jump to such high Mpix sensors from the only 12Mpix D300s and D700 have (right, they started changing with the D7000).
I agree totally with you re. system constraints, and handicap due to lack of FF "pro" body in Pentax production.
If not done in the past, anyone to launch on this forum a pentaxian pool :
"Would you buy a K-mount Pentax full-frame sensor DSLR, or EVIL ?"