Maybe Dark Link is the same as Ghirahim, as in being one of his allies. Although Dark Link looks nothing like the Demon Lord, it's still possible they take all sorts of shapes.
A lot of this sounds like speculation, or facts based off our wildest hopes and purely made up. The bit where it states there's a dating sidequest sounds very fraudulent to me. They could be either drawing attention to themselves or messing with our heads. However, I won't deny there will be a...