What would make the GXR M mount module stand out relative to the NEX 7 is if they incorporate profiles into the camera module that would correct for distortions that occur when say mounting an ultra wide on the module.
I wonder if they would go that far though.
I personally feel that the main difference is that the Ricoh is designed to be a M mount camera right from the beginning whereas the Nex 7 is just an E mount camera with a third party adapter.