I have been told that Canon will be doing simultaneous live streams in the USA and Europe for the announcement of the Canon EOS R5 and Canon EOS R6 on July 9, 2020, if true, I suspect we'll be seeing a teaser for the event very soon.
The same source claims that the RF teleconverters will work with any RF lens (I'm not sure about this claim). I'm also not sure if things will work differently with adapted EF lenses.
I have also been told that there will be more “cool” adapters and lens add-ons coming later this year. I wasn't told any more than that.