I think your guess is perhaps a little low. Frankly I am a wee bit disappointed if this is true. I have the 300mm f4 and although long in the tooth it meets my needs at 300mm with terrific results. I also have the 70-200 VR1 and use it very successfully with the TC-14 making around 100-340 @ f4. I had hoped for a new 80-400mm. That said and although not perhaps a lens for lower light I also have the excellent Sigma 50-500 OS.
Many had hoped for a Nikon version of the Canon 100-400mm. It will be interesting to see how the 100-300mm f4 performs if the rumour is true.
If this lens comes out, I would guess it will be at least twice the price of the 300mm f/4 AFS lens. This guess is based on the typical ratio between zoom lenses and primes of the same speed, i.e. 180mm f/2.8 vs. 70-200 f/2.8, or 60mm f/2.8 vs. 24-70mm f/2.8, etc. It will also be much larger and heavier. I'm not interested. Make a 400mm f/4 prime instead.
It seems that there was a similar thread in Nikonians about Nikon filing patents. At least one person stated that this meant very little, since Nikon files quite a few patents without actually manufacturing the item. I don't know whether this is true or not. Jim http://www.jimsack.com
Yes, I've heard that too. Like you I have never had it confirmed, but I guess it's the design which patented to ensure it's not snatched. Of course, Sigma had a 100-300mm lens which is now out of production, so perhaps this one is being registered so they can prove design differences. I remember the arguments between Sigma and Nikon regarding Sigmas OS and Nikons VR.
Nikon files for patents in the thousands (almost 14,000 at the USPTO from 1976 to date), and it may take years before a product is produced using such patent.
For Nikon lenses about 7,400 patents have been filed if I recall right.
For example, the VR for a lens patent was filed in 1994 (at the time the compact VR camera was introduced to the market), however, the first VR lens (80-400mm) was not released until 2000, 6 years later.
Also, "image-capturing method for executing display of a live view and a focus detection operation simultaneously" was first filed in 2003.
I haven't had the time to search for the 100-300mm lens patent but in my experience it may be a while to get into the shelves, even if confirmed.