Sony is trying to push the A9 into the sports arena. A pro level EOS R will be measured against the latest A9, so I suspect that it will be positioned as an attractive upgrade from the 1Dx2, but not a true competitor of the 1Dx3. (This does put mean that the EF to RF converter must preserve the image quality and focus performance of existing EF lenses.) I'm still expecting an Rx to make some sort of splash at the 2020 Games. If so, it has to be a sports body.
I remain hopeful that the pro R will be a mirrorless 1DX3 and that Canon doesn't see the need to force people to choose between either the true flagship body or else the best glass (RF), but not both.