http://nikonrumors.com/2011/05/05/rumor-nikon-mirrorless-camera-will-come-with-three-lenses-and-2-6x-crop-factor.aspx
But if you also look at the illustration diagram in the above post, you will see that the rumoured Pentax mirrorless, which has partially been confirmed to be true officially by Hoya recently, will have a nearly smallest sensor which is actually rather tiny:-
That must be really "great" afterall! >:-o
Read Also:-
Comparison of Sensor Specs - 645D Against Others
Sensor Size of the 645D (and More Technical Talks on DSLR Form Factors)