It's only money. They're making peanut butter and jelly sandwiches very tasty these days and you can probably live off them for a few months, lol.
After watching a few a9 videos and then listening to the a7rII shutter clank it makes me feel like anything outside of silent shooting seems like a dinosaur.
The a7rII has a silent shutter, and the a9's mechanical shutter sounds a lot like the a7rII. There are many reasons I wouldn't use the silent shutter...mainly because very often I use speedlights, and speedlights do not work with silent shutters.
Also with regards to using the a9 for weddings/events (which is what I'd need it for as the a7rII is better for everything else), because I often need speedlights, 20fps and a huge buffer don't matter because you have to consider the recycle time of your lighting equipment....so its more a matter of timing your shots at key moments than firing off continuous bursts.