More Nikon D600 specs website admin say's this is 60% likely.
-39 AF points (with an option of 11 AF points)
-5 fps (same as the D700, the D800 has 4fps)
-2 SD card slots with Eye-fi support
-Build-in retouching images functionality
-Built-in flash with sync speed of 1/250s
-Two user settings: U1 and U2
-Fn button
-GPS
-HD video
-The sensor inside the D600 will probably be 24MP (made by Sony, modified by Nikon)
-The new camera will be marketed as an entry level full frame camera
-Auto DX crop mode
-In-camera RAW editor
-Built in time-lapse functionality
-Possibly with build-in HDR
-Possibly with integrated GPS
-New external battery grip
-To be released this summer
-The D600 will probably not have an internal AF motor, which means it will work only with AF-S lenses (just like the D3200 and D5100)
-The price of the D600 is rumored to be very low - maybe as low as $1500
-Announcement before Photokina (September 2012)
-One or more low-priced f/4 lenses will be announced with the D600. For example, Nikon recently filed a patent for a 24-70mm f/3.5-4.5 full frame lens which seems to be designed for a cheaper FX DSLR body
If this is is true then damn, it would be a great step up for APS-C users, I don't have any AF lenses so I can live without the AF motor.