Sony engineers: "Challenge accepted"
In terms of performance and operation, I don't see how things could get much better than the a9 though. I've been shooting a bunch of random stuff of my kids because I have nothing else to shoot right now....but seriously its a camera that will never hold you back operationally. Very responsive camera that is effortless to use.
Have you experienced the "can't go back" syndrome yet? A lot of a7rII shooters that once they shoot with the a9 for a little while seem to be feeling a sense of primitiveness when going back to the a7rII.
A good friend of mine is an a7rII shooter for the past year or so. Put maybe 30,000 shots on it. He rented the a9 last weekend to see it was, he just told me that the a7rII is now traded away and he has the 70-200 f/2.8 GM coming in now with the money he got for the a7rII. He was like after shooting in a quick 8-10 shot burst with the a9 and then trying the same with the a7rII, he waited for his toast to pop up while the rII wrote the files, exaggerating of course.