Within the decade Canon USA disclosed in a video & written presentation that the 1-Series body makes up 1% of all SLR sales.
I've been looking for it on Google, Canon.com and YouTube but it appears to be removed already.
So far
Ken Rockwell stipulates that the body is 1%
Because of the price bracket R1 that will be north of $4,000 & it will cannibalize $6,500 1D X Mark III sales.
Sony and Nikon does not have a MILC & SLR flagship body at the same time because the market too small.
Photogs need to look into the business side of selling of cameras when weighing any rumors published on this website.