We're told that Canon mentioned the replacement for the EOS 5DS / EOS 5DS R in an internal presentation last week. The camera is scheduled to be announced in the first half of 2019.
The presentation only mentioned one camera body to replace both the EOS 5DS and EOS 5DS R. I don't think this change in the line-up would surprise anyone
Canon is still playing around with their 120mp APS-H image sensor, and a big resolution bump in an EOS 5DS follow-up would be nice.
No specification information is available this far out.