The comics haven't even fleshed out his origins. What hope would WB have? Regardless of who is at the helm.
Failed comedian from a broken home turns to organized crime to make ends meet as part of the red hood gang when he's cornered by Batman and falls into a vat of chemicals. First third of the movie.
Second act is his rise in Gotham, him carrying out a bunch of plans that work but ultimately bored by the lack of challenge in the underworld. Starts doing more brazen crimes for attention like sending playing cards and announcing his plans. Ultimately finds the most fun in his conflict with Batman. He's goes after the people close to Batman like Gordon and his Family, threatens all of Gotham, etc.
Finale is the kidnapping and torture of Todd as the last big act against Batman. Leaves a Ha ha Ha stained Robin costume as a clue for Bats as well as other breadcrumbs. Batman arrives at the location as it explodes. Batman, shocked and upset, hears Joker's laugh and heads towards it. Movie ends with Joker in Arkham meeting harley.
An origin story with the little bit we know about Joker that sets up red hood and ties into Suicide Squad/BvS/Batman....oh wait, elseworlds tale. Forget all of that then and just make him a literal clown that, I dunno, gets shot with an alien make-humans-crazy beam or something.