…the Twain revision allows teachers to teach what Twain meant, as opposed to what we think of when we hear the word.

Roger, that word was just as much a slur back when Twain wrote Huckleberry Finn as it is today. Twain meant it that way. If you in fact want to teach what Twain meant, then you need to include the word. Substituting "slave" is pitiful.

What the publisher should have done was leave the text as is and include a forward that would explain the history of the word, the harm it's done, and why it's as horrible as it is.