My predictions.

D400 24mp FF to compete with the Sony A900 (both same size)

D4 26-32mp FF to compete with the new Canon and to have more mp than the smaller Sony A900. Or maybe a 24mp with 8-12 fps capability.

If Nikon puts anything smaller than 24mp in the D400 it won't be able to compete with the Sony A900 with it's 24mp FF sensor which also has in body VR.

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'Speaking the truth in times of universal deceit is a revolutionary act.' ~ George Orwell, '1984'