I am a canon 1dx ii shooter, Sony A7 and Fuji X series shooter. I've also had the priviledge of shooting the A9 at Sony launch - I wrote this feedback on Sony alpha forums shortly after I had a chance to play with A9 for a bit : https://www.talkemount.com/threads/hands-on-with-the-a9-a-disappointment-for-me.16912/ In summary - I do feel that the A9 is massively overhyped. It is a great camera however there are many tasks for which I feel an XT2 is the superior camera and vice versa there are some tasks where I feel the A9 is the better camera.
Some things to keep in mind when perusing the spec sheets....
- A9 in any form of continuous raw, bracketing, HDR etc... falls back to a 12bit read out (note the difference between read out and file format - i'm not talking about compressed 11+7 file format). This is the same with the a99ii, a7rii, a6500, etc.... Sensor measurements on DXO typically are found based off of single shot mechanical 14bit read out. It appears that this is a design decision to prioritize FPS over maintaining quality.
- Quality loss in 12bit mechanical continuous mode vs 12bit electronic shutter continuous mode is an unknown quantity on this camera right now. What we do know already from the a7rii and Jim Kasson's measurements of existing Sony bodies is that there is a qualitative loss in noise and dynamic range going from mechanical shutter to electronic shutter (outside of the 14 bit to 12 bit loss). Whether that is significant for your purposes, noticeable or not is a subjective perspective and each to their own. Nevertheless it's good to be aware that electronic shutter (same with XT2) does come with a performance penalty, however from comments in Jim Kassons thread on dpreview it appears that Fuji does not play with the read out bitrate to achieve their continuous/bracketed speeds. 14bit all the way through. Fuji, Canon, Nikon all continue to read out at 14bits in continuous.
Why do I mention this? The A9 specifications look good but need the background context of how they are achieved to really give an apples to apples comparison with pre-existing workhorses. Overall a camera is more than the sum of its individual specifications. Case in point: in mechanical shutter mode the a9 the continuous framerate is the same as it's older brother (the a7ii ) and works at a respectable (for my needs anyway) 5fps. Mechanical shutter mode on the a9 is the only mode that guarantees no banding in phosphorous lighting conditions and no jello effect with fast moving panning subjects. The electronic shutter mode on the a9 does handle panning subjects somewhat better than the electronic shutter mode on an XT2 in my brief experience but that difference isn't huge. BUT - the a9 electronic shutter mode does not eliminate the problem entirely so regardless of how improved it is, read out rates are not fast enough yet to achieve banding free and no jello. Maybe the solution is for Sony to drop the bit rate further to achieve faster readout in the next generation? If you need to use fast flash sync, cannot tolerate any potential banding in phosphorous artificial lighting, no tolerance for jello - mechanical shutter is still the name of the game regardless of camera brand preference. In the context of mechanical shutter capability, the 11 FPS (continuous) with boost grip on an XT2 with 14bit read out (or the 11fps of the a6500 in 12bit read out) will in theory at least be a more realistic body if you shoot in these types of conditions. Pragmatically though, if you are considering spending 6k on an a9 then you probably would be better served again with a D500, D5 or 1dxii with fast mechanical shutter in my opinion. If the purpose of the camera is for weddings and situations where you CAN use the electronic shutter, then the A9 is a great camera but there are equally capable cameras in my opinion for less money - you can buy two D750's + change for the price of one A9. You can get 3 XT2's etc... If you click through to the link I mentioned earlier you will see a video that I shared immediately of my first hands on experience with mechanical shutter. A 1dx or D5 will give a superior experience in such high speed mechanical modes. I confirmed with Chris and Jordan during todays TCS live show the slideshow effect in mechanical with their sample too. Also confirmed today with Chris and Jordan is the 12bit and phosphorous lighting limitations. My personal take away is that the A9 is a great camera - heck there are LOTS of great cameras available. Just do your homework before abandoning any ship or declaring X better than Y. You may find that the compromises the A9 makes do not work for your shooting style.
Just my 0.02