The Nex Cameras are mirrorless, and that allows them to be smaller and thinner. This is due to a reduced flange distance.
Sounds like it could handle E-mount lenses in crop mode, and would need alpha lenses for full-frame. Which is really actually good for users, cause Sony has some good A-mount lenses, where as I can't imagine any E-mount holding up to full frame. But with a crop mode, they'd be the same as they are on the NEX-7
A-mount lenses and a E-mount lens have different flange to sensor distances, so a adaptor would be needed to adapt aA mount lenses. If the Camera was designed to use A Mount lenses, then it would need to be the same thickness as a DSLR, and e-mounnt lenses would not work, since they would have to mount inside the body to focus or have some sort of a adapter that had optics and made a poor lens really poor.
If A FF Nex were to appear, it would need all new lenses.