A NikonRumors.com reader did some pixel-peeping on the Nikon lens roadmap silhouette images and determined some new aperture information by figuring out the width of the objective lens elements.
The coming 800mm lens will likely be an f/6.3 lens, sacrificing a little aperture for some size reduction. The 400mm lens will, as expected, likely be an f/2.8 model. The 200-60 zoom is likely to follow the Canon trend in allowing the aperture to creep up above what was previously considered the territory of high-end glass to an aperture of f/6.3. The 600mm lens will, of course, stick to the f/4 standard.
The choice between running a 600mm f/4 rig with a teleconverter rendering an effective 800mm f/5.6 versus using than 800mm f/6.3 would wind up being an interesting balance. Whether one or the other is superior will likely come down to the degree the teleconverter reduces image quality beyond reducing aperture.
The improved quality of Canon’s Mark III teleconverters is likely the reason why Canon has skipped the last two generations of redesign fits venerable 800mm f/5.6, as the very-highly-regarded 600mm f/4 mostly outshoots it when sporting the new 1.4x teleconverter III.