I went and ordered one :grin:
For me it is not about features that are still missing or how it could be better. It is already better than what I own and that is enough. I've long waited for a better AF and a faster drive and now I have both. Add to that the IS, the dual slots, pixel shift which are all icing on an already good cake.
Call me crazy, but on my trips I always take the A7RII with a mid-range zoom (24-70 type) for the wider, habitat type shots of the animals and have missed the fast AF and fast frame rates. Of course I also have the long zooms (70-200 and the 100-400) mounted on the A9 bodies. In an evolving situation, the animals could come very close to you and then you have too much lens with the longer zooms. Until now I found I was missing a lot of the shots due to poor (relatively) AF of the MkII body and also, the continuous shooting was not available in silent shutter mode.
Even with the longer zooms on the A9 I find myself cropping into the image quite a bit. For BIF that leaves very little to play with. Now I can pair the 100-400GM with the A7RIII and still get a) spot on AF during flight, b)fast frame rates for a variety of shots and c) enough resolution to be able to crop 50% of the image and still get a decent sized print. That eliminates the need for longer tele lenses - until the new, ultralight 600 f4 comes along
At the end of the day, if a camera can take the images in the situations I am in and deliver the image quality, it is all I want. Each new version brings a few more refinements. Whether those are enough to make one upgrade depends on factors other than the purely technical. For me, it is enough. YMMV.