I am in the "no idea" category, although I have a bit of an idea. I will eventually replace the 5DIII, but I am not in a rush. When I do replace it I will want AF points that are f/8, EV-3 or EV-4, and that have the best possible spread (quantity is less important than quality). I shoot stills, so video features mean very little to me. I consider the 5DIV to be 20% better is about 15 different ways to the 5DIII, which becomes a nice upgrade. Yet, I am very happy with the 5DIII and do not really consider it deficient. Of the upgrades, I do occasionally battle shadow noise/banding on the 5DIII, so the improved sensor and finer grain noise would be an upgrade. I would want extra fps, but 7 fps on the 5DIV isn't that much motivation compared to 6 fps on the 5DIII. I don't really feel the need for 30.4 MP, so if Canon backs off on the MP and gains in sensor performance, I am all for it.
So, I can see myself getting the 5DIV after the prices fall a bit, getting the 6DII if the sensor is great and it meets my AF point requirement, or deciding to save my money for classes, excursions, or something like a 500 f/4 II.
I have about 52,000 actuations on my 5DIII, so it should be good for years. In the mean time, my bank account grows.
If Canon were to make a camera just for me it would:
- 28 MP
- 30-60 high quality AF points covering 80% of the frame
- 9 fps
- Better shadow noise/DR/less banding than the 5DIII (newer sensors seem to be what I want)
- Take whatever I can get at higher ISO
- wi-fi
- DPAF or something else that improved Liveview focus
- Touch screen that allowed you to select AF points on the LCD while looking through the viewfinder (seems like a great feature on the M5)
- Built in intervalometer, focus peaking, etc
Really not that far off of the 5DIV.