As I understand it, Thrawn is a TV show character first and foremost now, so Dave Filoni and co. are the ones that get the first crack at any future story with him. Whether that will happen or not remains to be seen, but the people working on the cartoons were huge fans of the character, so maybe?
Why would he be a tv show character "first and foremost"? He's starred in three books, and was originally a book character. He's no more a "tv character" then, say, Obi Wan Kenobi is. Also, Dave Filoni doesn't run Star Wars, so its not really up to him. the people who "get a crack at him" are whoever makes a pitch that the actual people running the brand think is worth doing.