Some other problems with it are that they've specifically referred to him as Bruce Wayne in articles and such. Plus, they've been eyeing Joe Manganiello as Deathstroke for Suicide Squad. However, he never joined the cast, but Scott Eastwood is in the cast, and he's been rumored to have taken up the role. David Harbour is also in the movie, and he looks like he could even take up the role of Slade.
The Joker as Robin part I can buy. But not as John Blake. As Dick Grayson. They're taking a lot of inspiration from Frank Miller's Dark Knight Universe, and were Joker actually Robin, Dick Grayson would make the most sense. Dick Grayson was a villain in The Dark Knight Strikes Back, and he pretended to be the Joker for much of the comic.
But this whole "Batman is actually Slade Wilson"? I just don't buy it at all.