Sooooo, I had a go today.
It is amazing.
The no black out is almost the best thing since sliced bread..so to speak, I am not sure if it is necessary but it is certainly nice.
The AF tracking with native lenses are really fast, one thing I didn't look into is if I can use a single focus point because you can move the little box with the thumb stick to focus, it still comes up with a cluster that darts around when you press the button and a couple of times that focus point cluster popped up on the other side of the EVF!!! totally assumed wrong what I wanted to focus on. It has very very good AI servo though.
Also tried it with the Sigma adaptor with my Sigma 50A 1.4. The focus speed is definitely slower compared to the 24-70 GM or the 85 GM.
The shutter, as in FPS is insane, was instantly taken back how quick it is. With the 5D I could have it on Highest speed and I am able or used to press the trigger and have 2 or 3 photo bursts, which I am used to, in order to eliminate blinking, same process with the A9 and I think about 6-7 photos went off. I would go through SOOOOOOOOOOOOOO much memory if I am shooting that thing.
Overall, from a quick play I like it a lot, it does a LOT right, with native lenses it works brilliantly, size wise with the primes and adaptor is a bit big so I won't go into the size is smaller than a DSLR argument as it is moot.