Origin films have become quite popular in recent years and the Joker would be perfect for such a platform. The character has had many different versions of his back story told, so it will be interesting to see what the newest iteration of that will become.
Scott Silver is said to be co-writing with Phillips, and the film is said to take place in the 1980s with a grittier feel than most comic book films.
The Joker was most recently portrayed by Jared Leto in "Suicide Squad" and most likely, he will reprise that role for "Suicide Squad 2".