We're told that most of the mirrorless hype will belong to Nikon ahead of Photokina next month. A solid source is saying that no official announcement in regards to a full frame mirrorless camera from Canon will happen before Photokina next month.
While we couldn't confirm an announcement date, we're told that October 2018 continues to get mentioned as a possible month in which Canon will address mirrorless. Though that may not necessarily mean an announcement for a full frame mirrorless camera.
There is still the possibility of a development announcement for a full frame mirrorless camera.