Nikon is rumored to be currently working on a new full frame mirrorless camera. Here is what I know so far:

full frame camera

mirrorless / mirrorless-styled

the camera will be small (about the same size as the Olympus E-M1)

E-M1) no EVF

regular F mount

currently being field tested

Another hint that in a way confirms this rumor is a this recently filed Nikon patent for a 28-80mm f/3.5-5.6 VR full frame mirrorless lens.

In interviews with AP and dpreview last year, Nikon executives said that a new large sensor mirrorless camera is a possibility in the future.