I got this email from a reader and after a brief investigation of the source I feel comfortable to post it here - I have no way to confirm the validity of the rumor, but I have a reason to believe that the source is trustworthy:
Whilst surfing the web I came across your site and saw the comment on the Nikon D4 and that there will be no such middle format Nikon camera, this is incorrect, thought I'd fill you in on some details.
Nikon will be bringing out a middle format camera by the end of the year, which indeed is the so called "The Big" D4.
This information has been confirmed to some pro photographers as well as Nikon distributors, camera will have a CCD size of 55x55mm, there's no exact details on final resolution yet but it will be somewhere around 50Mp, quite similar in design to that of the Leica S2 camera system which was announced six months ago.
New lenses for the new middle format camera will be announced which will cover the larger format as well as lens specific extenders/adaptors which will allow those standard FX lenses to be used on the D4, these adaptors will convert standard FX lenses to cover larger image size such as that of D4 but will not have the true optical quality such as those designed specifically for middle format Nikon D +++ cameras to come in future.
For the time, no detailed information on full range of lenses are available but planned for the release together with D4 are the 35mm, 80mm and 180mm lenses along with the 0.7 retro-adaptors for standard 35mm Nikon lenses.
Pricing has not been set but since this will a full breed pro camera, expect pricing to be in the $30.000,- to $40.000,- USD range, (Euros in Europe) so no reason for amateurs to get excited and go wild about it!
No rumors, facts...