I'd love to see K'Kruhk make a cameo. He's a legendary Jedi who's been arround since 5 decades before the Battle of Yavin. And his design is based on those old Samurai-masters, with the hat and all.
Qu Rahn would be nice as well, to explain what he did between Order 66 and the Dark Forces time.
And Empatojayos Brand would be cool as well. We know Darth Vader left him for death, so a revenge storyline could be a nice addition to the story.