Wow, I had the chance to play with the camera today for an hour. I'm really impressed.
20fps: You can document the closing of an eyelid now. You can't miss the right moment with this camera.
focustime: With the 24-70/2.8 GM there was no focustime. No matter if there was no contrast or I changed from far away to a very close subject. The light in the shop was not very good too.
AF: It's on track all the time, even if something block your sight for a short moment, it finds the original subject. people can turn around frast, change directions quickly, but the AF is spot on.
Eye-AF: I did 20fps with 1m distance of a face and zoomed in from 24-70 quickly at f2.8. Not every shot was perfectly sharp, but you can see it only when you pixel peep.
face-detection: It recognizes faces that are smaller than one focus point! Even if a part of the face is covered or be seen from the side. This is just night and day to the a7rII, which isn't that bad at all.
EVF: Reviewing feels very close to a display at home. brightness, contrast, sharpness and colors are very good. Under artificial light you may recognize a slight flickering while shooting 20fps. It's because the framerate drops from 120/s to 60/s.
lags: everything is much faster than with th a7RII: start up, writing, review,...
button-customization: you can customize everything! the setup-menu is very clever. You can skip through groups of functions instead of a long alphabetical list. there is even a customize function for all things in review-mode.
video-AF-AEL button: I'll switched the AEL button to eye-AF and was happy with these three buttons. Depending on the situation I can now choose between all three (video, AF or eye-AF) directly.
AF-Mode wheel: a good addition.
joystick: I had some issues to switch the AF point with it. But you can also just push it and then use the touch-screen to set the new point.
new G-X1EM grip. A great accessory for bigger hands. I putted it on my a7RII aswell. I will buy one, or a cheaper copy of another brand (I'm sure someone will do it because this peace of plastic is ridicously expensive).
size/weight: There was no difference to the a7RII unless I was concentrating on it. The slightly bigger grip is the only noticeable thing.
a7RII or a9? It's really depending on the image quality. If the a9 is on par with the a7rII it's only the MP and the s-log on the a7RII. On the other hand, if you don't need the AF-capabilities and fps the a7RII has it's MP and price advantage.
For people that like to shoot people/animals in action (esp. in low light) the a9 will be a big step forward.