This is great news and should help solidify the DCEU.
I hope this isn't the start of a stand alone trilogy, however. I think two solo movies will be plenty sufficient as he'll supposedly be making appearances in all the other movies.
I will say what may be an unpopular opinion, but I hope the movie isn't solely focused on the Joker. At least have some other enemies not as often explored or who've never seen the big screen at all.
I would prefer a Hush focused storyline, or even The Court of Owls. Heck, I'd be down for a more loyal take on Ra's al Ghul.