This is a great idea! I'd be on board.
Question for you: what do you think of the new Batman movie(s) being part of the "DC Black label"? I doubt WB would do it, as Batman is one of their cash cows and they'd want to make the movies as accessible as possible, but as we all know Batman more than any other major comic character lends himself well to that kind of tone. I also desperately want Reeves' Batman to be connected to Joker, even if the characters obviously never cross paths. I like the idea of Fleck's Joker being the original inspiration for another Joker who goes on to become Batman's foil.