While it seems obvious that Dark Rey is a "vision" or nightmare, I do feel the need to point out that--in the context of that article--"vision" does work as a synonym for sight. It might have been changed simply because the author realized that their attempt to sound sophisticated made the article read as a spoiler.
However, Dark Rey almost certainly isn't real, so there's that. You really have to go with the Least Common Denominator with this trilogy (and Star Wars as a whole, though less so overall). JJ Abrams loves to tease his audience with cool, mysterious things that never pan out, because he's an expositor. He builds up mystery, tension, and exposition that he doesn't have solutions for, which is why almost everyone hated the ending of Lost, not because the ending itself was bad for the characters, but because it was the most obvious, expected ending for a series which had cast itself as something new and unpredictable.
IMO, the same thing will happen with TROS and the Sequel Trilogy. It'll look cool on the surface, with great action, great visuals, and even great acting, but under that surface it will end up as a jumble of missed opportunities, unsolved mysteries, and unfulfilled expectations.