First of all, he has got to be kidding. I love me some Oliver Stone but the only reason Jamie Foxx would be a likely candidate for this film is because of his massive popularity. Jamie Foxx shouldn't play Martin Luther King, he doesn't have the look, he's NOT the MLK look at all. Jeffery Wright would be the closest one and I only mention him because he already played MLK before and has more of a look, or at least closer to it... still not it and overall I would think that a unknown actor would be better, it's a chance for someone new to get into the acting 'ring'.
He isn't saying that the film is going to be made because he is currently putting a script together and doing research with the King estate. I do think it's a movie that has to be done and Stone would be the guy to do it because he's sophisticated enough of a director to do so and it's in his wheelhouse.
Stone does what he wants and this is pretty clear but, I think he's the guy who should continue on a presidential biopic thing he's been on and do one on George Washington or some of the other presidents who need to be identified with today's audience, getting everything out into the open and cleaning up the mess that history has made of them.