Mysteries of the Sith
touched on some of these ideas, Vagabond. I do believe Mara Jade faces her own evil twin in Mysteries of the Sith
. I believe she also faces a corrupted, twisted 'dark Kyle.' Mara must decide at the end whether to fight and destroy her own friend, Katarn.
I am not sure we want to go down that path again
However, the concept of facing your own family or friends, who have been corrupted, seems pretty consistent thoughout Star Wars and the 'expanded universe.'
Still, I'd rather fight Thrawn
, evil military genius and plotter, and his henchmen, than kill my twin brother, who I don't really know.