Nikon Rumors has a great roundup about their thoughts, tips and suspicions surrounding what new Nikon gear should realistically be appearing in 2013.
The biggest rumor for most shooters is the fusion of the D300s and D7000 lines. NR expects to see a Nikon D400 or D8000 that servers as a successor to both lines with the Nikon D3200 and D5200 rounding out the low-end consumer market. Personally, I think this makes a lot of sense now that there is a higher-end amateur camera with the Nikon D600 that’s just a little bit above the D300s price range (based on the launch retail price). Accordingly, a D400 or D8000 model could now slot easily between the D300s and D7000 to answer the prosumer sports and wildlife call with its APS-C sensor.
Additionally, NR expects a higher resolution full frame model (the D4x?) toward the end of 2013 that would likely be situated above the D4, and would use a 36MP or 52MP sensor. A show of hands for who needs 52MP please?