There are some photographic disciplines where f/2.8's weight and bulk are simply excessive. I'm sure I'll be corrected on this, but motorsports is a great example of why an f/4 lens is plenty. Unless one has to do a night race (definitely the minority), there's pretty much no using the f/2.8 capability, since shutter speeds are mostly capped at around 1/250th and most of the cars don't even have headlights so they can't go anywhere near dusk. In fact, it's common to shoot at lower, out of range ISO just to stay with the wider apertures. With VR there's no reason to go to f/2.8 in the paddock either. Even in the rain the light holds up well enough to use an f/4 lens with ease. Even on an old DX body where ISO is limited to 800.
I will admit that I wish it were priced rather lower. I won't be getting one of these unless the price comes down a fair bit. Maybe in several years I can get a used one, especially if I sell my 180/f2.8 AFD...
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!