(Did anyone else get the impression that the EU stuff might be Jon Kasdan’s work?)
And yeah, I think all the EU stuff was Jon mixed with some consultation with the Story Group.
Well, apparently the Darh Maul cameo was in fact Jon Kasdan’s idea;
No direct mention of the story-group getting involved though, but that hardly proves that they weren’t involved in one way or another. And Jon Kasdan is described as “a particular champion of Darth Maul”, implying that maybe someone else, most likely the story-group, had tossed around various ideas and suggestions prior to on settling for Maul.