Legacy lens compatibility? about possible future FF emount camera.

It would most likely work like DX lenses do on FX Nikon full frame cameras. The sensor would switch to "crop mode", and you will shoot using the middle of the FF sensor that corresponds to the size of an APS-C sensor. This is already demonstrated with the VG900 Full Frame E-mount camcorder. However, just like the VG900, expect there to be an option to turn off this auto cropping. So you can capture a full frame image using a crop lens, but of course you will see a circle in the middle ... or almost a circle.