On television we've had a half-Japanese actor play Superman and a half-Chinese actress play Lana Lang.
This really isn't the same. Lois being African American is a significant change given the history of the character. I think it would be interesting and could be a wonderful thing as long as the film makers understand the weight of such a change...Lois being black would impact the character...hopefully it would do so in a positive way...but the film makers need to understand that impact. it isn't something that should be taken lightly.