I'll lead by saying that a replacement for the Canon EOS 5DS R will not be coming in 2017, this is potentially a Q3/Q4 2018 camera.
Anything this far out is generally considered unlikely to come to fruition, but there have been exceptions and specifications always evolve and change for camera bodies.
This is what we're told about the EOS 5DS / EOS 5DS R Replacement:
- Working prototypes are currently being tested.
- The “5DS” series will be amalgamated into a single camera.
- No low pass filter.
- All new 60.1mp image sensor.
- A new type of low megapixel mode.
- 4K video (video features will be basic)
- Identical body to the EOS 5D Mark IV.
- Focus peaking present, may appear first on another DSLR.
- Expect all the other features such as DPAF, Wifi, Touchscreen and GPS.
We've heard other rumblings about a high megapixel replacement, and that these cameras won't be on 5 year product cycles. I too expect to see this new camera some time in 2018.
*Update 09/04/2017 @ 16:56 EST: Keep in mind that Canon uses APS-H sensors in some test bodies and this can affect pixel count.