While I think the showrunners are hacks, the overreactions to this are pretty laughable. There are multiple (talented) black writers involved (which you'd know if you read the article instead of clicking "post" immediately). The general idea isn't far off from Man In The High Castle and various other alternative history sci fi/fiction concepts from the last...70 years. And while I dislike Benioff and Weiss, they aren't alt right idiots. That has nothing to do with the show, and I'm going to assume the theme of the show won't be sympathetic to pro-slavery views.
I have a feeling the show will be an attempt to fabricate the complexity of Game Of Thrones' characters with lazy "grey" characters...like sympathetic slave owners, a black slave owner, poorly done Nat Turner-type rebellion figures, etc. But hey what do I know, we don't have any details or character lists.