I always wanted to see Kyle Katarn on the big screen. But if I really had to pick someone, Dash Rendar. Disney really screwed up in their data mining of the EU. I would like to see Steve Perry come in and do a screenplay adaptation of his novel, Shadows of the Empire and we get either a Clones Wars style animated movie or a 13 episode series adaptation. After which, a new movie series could be done with Dash and it wouldn’t hurt any of the original movie canon and since his only canonical appearance (since Disney’s take over) was the book A Solo Story: Tales from Vandor, Disney would have more freedom in developing the character without much risk of screwing him up (though they probably would anyway).
Plus it would be nice to see Xizor and his rivalry with Vader played out on the tv.