The @camerainsider Twitter account has been consistently wrong with previous Nikon rumors but they did however correctly report the announcement date of the new Nikon Nikkor Z 600mm f/4 TC VR S lens (a few days after my blog post) but did not mention the Nikon MC-N10 remote grip.
CameraInsider now reports that tonight Nikon will announce a new black Zfc camera and a Nikkor Z 40mm f/2.0 SE lens (probably in retro design to match the black Zfc, since that lens is already available).
There was some talk a while back about a black Nikon Zfc camera (see pictures above), but I have not received any information since.