When Michael B. Jordan was cast as Johnny Storm, I was against it but not because he is Black. (So am I.) My objection was that Sue was not also played by an African American. Making Sue adopted made having a Black Johnny and Franklin Storm seem like a stunt to me. Trank was telegraphing how edgy and different his version of the FF would be, but he didn't have the courage to include an interracial relationship/marriage in his film. There are any number of talented Black actresses who could have played Sue, not that I would have wanted anyone I admire to get caught up in Trank's disaster flick.
Of course, in the MCU Fantastic Four, we can expect to see Storm siblings who actually have a relationship with each other instead of strangers who never speak. Not to mention a team that feels like a family, as in the comics.