If I had to name the frontrunner now it would be Birth of a Nation. Trailer was released this past week.

Release Date: October 7, 2016
Summary: Nat Turner, as a slave boy, is taught to read so he can study the Bible and be a preacher to fellow slaves. When Turner’s master takes him across the country on a preaching tour to profit from his preaching, Turner begins to see the scope of slavery and decides to become a different leader.
Director: Nate Parker
Starring: Written, produced and directed by Nate Parker who also stars as Nat Turner. Also stars; Armie Hammer, Aja Naomi King, Jackie Earle Haley, Penelope Ann Miller, and Gabrielle Union
Reason for being an Oscar Contender: Premiered in competition at the 2016 Sundance Film Festival on January 25, 2016. Fox Searchlight Pictures bought worldwide rights to the film in a $17.5 million deal, the largest deal at the film festival to date. At the end of the festival, it won the Audience Award and Grand Jury Prize in the U.S. Dramatic