According to a report in the Nikkan Kogyo Shimbun, one of Japan's primary newspapers, Canon will introduce a truly professional EOS R system camera in 2021.
In the report, they also state that early prototypes have already been manufactured and are in testing.
The article also suggests that it's going to take Canon another 3 years to get the RF lens lineup to match up with the breadth and depth of the EF lineup. This seems quite likely, lenses are not easy to engineer and manufacture.
Canon also mentions that they're working on a converter/adapter to turn a mirrorless camera into a DSLR.
We are also developing a converter that can join a mirrorless camera to an interchangeable lens for a single-lens reflex camera.
We're not sure how that's going to work, but Canon News reminds of a patent from back in January 2018 that may give us some clue as to what they're working on.