I've just done some postulating on The Batman thread, and I came up with this:
QuoteThe Flash is set to be directed by It film-maker Andy Muschietti after Dope's Rick Famuyiwa left the project in 2016. The plot will allegedly ignore the two Joel Schumacher Batman films and continue on after Batman Returns.
Which means it's the Batman 1989 universe.
However, since Alexander Knox was in Crisis on Infinite Earths, that universe got destroyed. Ezra Miller's Flash was in Crisis, so it stands to reason it's canon of some kind. So... I don't even know where I'm going with this.
Maybe Flashpoint will reference the Crisis, and Ezra Miller's Flash will go back to a point before Crisis happened, and blow the whole multiverse wide open again?