I'm a little surprised by the enthusiasm for the 200-600, given my own experience with the 200-500. I purchased and sold that lens *twice*, because it was too heavy and too clumsy for what it did, and spent 90%+ of its time at max anyway - 500mm. Which made the 500PF a far better choice for me. I understand the Sony enthusiasm for their 200-600 a little more, since the long lens choices in that ecosystem are relatively more limited (not bashing, just observing). The 200-600 may turn out be a stellar lens, but to me the preferred kit would be the 100-400 and the 500PF (with TC) (or 800PF, which I haven't tried). Especially given the remarkable results people are getting with the 100-400 +TC1.4. I'm not a candidate for the 400PF (unless there's something really remarkable about it like a built in TC) since I already have the 500PF, but it might be a great for someone who doesn't already have the 500.
I have actually used the Tamron 150-600mm (G2) quite a lot, as I found it sharp and easier to handle than the Nikon 200-500. I also liked the additional reach. Unfortunately, my copy of the Tamron has proven unreliable; it has gone off to New York twice now for warranty repairs, first for the autofocus mechanism and then for a sticky aperture. The Sony 200-600 focuses and zooms internally and is actually pretty easy to handle; my assumption (or hope?) is that the Nikon version will be similarly ergonomically superior to the 200-500. I understand what eaj101 says about this kind of zoom usually being used at maximum focal length. But there are many situations where suddenly one needs zoom back to accommodate a wider view; even if this is only for one photo out of ten or twenty, sometimes you NEED that flexibility without having to change lenses.