Oh man, no one asked for "N-word" discourse on Twitter (of all places) but it seems we've got it. My sense is the use/mention distinction is deeply relevant, but not as illuminating as one would hope when abstracted from all contexts.
In other words, I know the inciting event for this permutation of discourse, but you're not gonna get a general theory of "When I can say the N-Word without Blacks getting mad at me." I think the individual losing his job has heightened the discussion.
But that does not mean it's a solid basis for elaborating generally what is going on with this particular slur. That is because social interactions, as we well know, are complex and varied.
Rather than making the assumption that one is either imbuing this specific word with occult power or that one is saying, "Let a thousand flowers bloom! Everyone gets an N-word (as long as you mention it
)". I think we should approach this more pragmatically.

I think it would be more helpful to breakdown in what cases mentioning is actually conducive to a successful social interaction and consider why or why not. We might find that there are scenarios where "mentioning" does not produce the desired social interaction.
And such cases would be worth knowing! I may be about to lose people but a Wittgensteinian approach of looking for family resemblances would make for much better discourse. I think this is a specific case where clarifying the complexity would be more productive than reducing it.
Or else this turns into another culture war about (whatever set of people [usually Black]) being too sensitive and yearning for the authoritarian policing of speech. I think we can hold both positions at once:
1) Arbitrary firing over the mentioning of a slur is not right. And 2) not all mentioning operates equally.
For instance, if a white "friend" is singing along with a rap song in my presence and insists on making eye contact with me every time they say "nigga" in the song (yes this has happened) I might start to wonder if this is a healthy social interaction.
I can always remove myself, but I wouldn't say, "They were only mentioning it and not using it." This strikes me as a relevant border case. I think the concern around "intention" is usually a distraction, but we should not pretend that others are completely opaque to us either.
Anyway, my point is we could do better with all of this. Instead of turning this into a general lament of "Now white people can't even mention N-word anymore!" Because the wretched of the earth these folks are not. We might, hopefully, get a better handle on language and respect.