I think many folks on this forum have the mistaken belief that the majority of camera owners are constantly looking to replace their current rig with the newest similar camera - either made by the same brand or by switching brands. I think those types are pretty rare. So, in my opinion, there will be no quick and fast migration from DSLR to mirrorless. I think most current FF camera owners (not forum dwellers) will most likely wait for the next generation - or even the generation after that - to make their next camera buy. That may be 2 to 7 or so years down the road.
The most likely buyers in the short term - it seems to me - are those looking to go FF who do not currently have a FF camera and those looking for a 2nd or backup FF camera. That is the target market at the moment, in my opinion. Because, as many have stated, there may not be enough reason to switch from DSLR to mirrorless at this time (despite the incredible internet hype) Most folks are not so gullible as to fall for all the hype (I hope).
For me, I do not have a FF camera, so I may be an early purchaser. It also checks my most important boxes: It has Canon color, it has an EVF for WYSIWIG exposure, it has touch and drag AF point selection. I'm also happy to see that the R will close the shutter curtain when turning off the camera to create a barrier to block dust when changing lenses. May be a small thing, but shows me that Canon is addressing the important details that others miss.