Well before Bryan Fuller announced that he was stepping back from his duties on the show, he outlined his vision for Discovery. He explained that his vision for the show would center upon a Lt. Commander of a starship rather than the captain, and that he wanted the character to be a woman. Speculation immediately pointed towards Angela Basset and Rosario Dawson, both of whom Fuller had previously praised.

It's possible that with Dawson and Bassett both tied in to shooting Marvel-based adventures in the near future, neither had space in their schedule. Then again, there are six more characters that need to be cast, so it's just as likely that Bassett and Dawson may find the time to head out to the 2250s.