It makes no sense to replace the 5D3 with 52 MP body based on the 7D2 sensor. +100000 Finally someone sensible!
The 5D3 is a great wedding/event/portrait camera and sometime sports body. While I don't shoot professionally, this is me. I'm not looking for more resolution, especially if it means a step backwards in high ISO performance. If anything, I'd like the 5D4 to incorporate the 7D2 sensor technology with larger, full-frame pixels for even better low light performance. AF during video would be a nice plus (even thought video is a more distant interest for me).
The 5D4 should also include a bump in FPS and buffer performance. I don't see this happening with 52 MP. All I see with 52 MP is HUGE RAW files, maybe 90-100 MB each. That's a lot for in-camera crunching and recording to cards.
I'll look at a 20 MP 5D4 with a nice bump in low light performance long before considering a 52 MP body. I still think the 52 MP body has a different audience than those who currently buy the 5D line. It actually makes more sense to put the 52 MP in the 6D2. But, it makes the most sense to spawn a new line of bodies for the high MP sensor.
That's been my thoughts for some time although I've never thought about the 6D2 in that way but you are correct.
I'm looking forward to seeing both cameras although the 5DIV would be the one for me.
The only thing that's niggling at me is the thought that Canon will split features such that there will be some thing only in the other camera that really should be in both ie something like an advancement in the RT flash system. Hope I'm wrong on that!
Happy new year to everyone!