An interesting anonymous tip I received few days ago (edited):
"For the last few months Nikon has been working on a carbon fibre body for a Nikon pro-level DSLR. They are specifically looking at the manufacture of a resin-infused 3D woven CFRP body as well as fatigue testing of some CFRP components. The body appears would be a full size (D1, D2, D3 sized SLR). The benefit of using carbon fibre is increased stiffness and a slight reduction in mass."