where does this misinformation come from and why is it sticking around? All rep gates for Nightborne have been removed in LEGION, there are some quests that require rep, but they don't unlock or block anything.

To unlock the nightborne, the achievement “insurrection” is required, this in turn requires completing all the chapters of Suramar, chapter 10/11, is “a change of seasons”. To access it, you must complete the quest “Redemption for the Fallen”, which reads: “Revered / Exalted Nightfallen”.

It’s not like it takes that long to get revered or anything, and by the time you do all these quests you’ll be at least revered anyway. But it’s does require a rep grind whether you want to believe it or not.