This is the kind of story you write if you want to shed a lot of prior continuity and refresh a character. They've done this with Thanos and Dr. Doom, where they say that prior incarnations in less popular stories were android doubles or clones. they even did it with the She-hulk, to nullify the X-Men issue where she got it on with the Juggernaut.

So, I suspect that part of the point here is to make a lot of the Joker's goofier appearances attributable to the Clown, now deceased. The problem is that DC isn't likely to forswear more goofy or problematic takes on the Joker in the future. We saw this same thing after The Killing Joke, where DC made no effort to keep the character at that level of quality. There was Death in the Family, with Joker running around the Middle East in a keffiyeh. We had the post Knightfall appearance, where he had long hair, a ball cap, dressed like a Miami tourist and acted like a movie producer, stuff like that.

This is a refresh point, but I doubt DC will make good use of it.