I think Antoine Fuqua is right to cast his Tupac biopic with unknowns.
I actually don't understand Hollywood's penchant for casting movie stars as real people in biopics. The hardest job of a film actor is to make you forget that you've seen them in other things. That is even harder for movie stars – assuming they care that deeply, which I don't think most actually do – because they have cultivated a persona that threatens to supercede everything else in the performance.
When you add to that playing a real person who may or may not have notoriety or with whom an audience will have some familiarity, casting movie stars just seems unwise. I mean, did anyone really see anything other than Leo in The Aviator or Reese Witherspoon in Walk The Line?
The Tupac biopic will likely be a standard biopic. It's unlikely that it will tell us anything new or interesting or revelatory about Tupac, especially given the fact that his mother is executive producing.
But in spite of that, Tupac himself could be the role of a lifetime for some young actor who can capture his great humanity without playing him as some weird contradiction the way he was characterized for so much of his career.
And the right performance can make even a bad film at least watchable.