Good question. Similarly, when will Hitler's mustache be able to make a comeback. It's not obvious. However, at a guess, maybe sometime after it has massively racist connotations (after all, we might not find it offensive to call the Irish chimps, but this was a stereotype a few hundred years back iirc); these connotations might start going, well, after the actual racism has. It's still used in a racist way. People are obviously aware it's used in a racist way. So, it's kind of hard to think that people would use it in a non-racist way instead of another word. So basically, after enough time has passed -- and society has improvedv-- for it not to have the obviously racist context it currently does. "Is this a forever thing?" -- history would suggest not... But since the civil rights movement is still well within living memory, it's not as if it's had much time to get there, so complaining about timeframe seems a bit disingenuous.