I'm now leaning toward getting both of them. Life is too short for me to concern myself with the cost of both lenses. I like the reach of one and the flexibility of the other.The 800mm PF is a terrific lens. It's ideal for small birds. But I have run into a number of situations where it is too long. In my case, the 70-200 and 400mm f/4.5 cover the shorter focal lengths and work well with the 1.4 TC. I probably won't get the 200-600, but I expect it to be a very good lens. It's likely to be an external zoom and variable aperture, which provides functionality and saves weight and size.
I expect Nikon to produce a lot of 200-600 lenses for the initial release.
As opposed to Kip, I find the 800mm PF is great for small birds that are small but active. But I have a lot of practice using the 500mm PF with a 1.4 TC, so the focal length difference is not a big issue. It's difficult - but I can be precise and focus on just a part of a bird and get an ID shot. Of course, field of view is very narrow and it takes practice to get used to finding the subject in the EVF.
Offense and defense, to cover all the bases.