If Dark Link was solely a creation of Ganon/Ganondorf then how did the wise man create him in AoL? And how about the dark link in Spirit Tracks?
A dark link fight would be epic, but as others have said, it may end up being too similar to Ghirahim.
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.