For the sake of argument, let's assume that this "Mara" who's being cast for Star Wars: Episode IX is indeed Mara Jade. It's worth remembering that this version of her may not necessarily resemble her original counterpart closely. Still, I would hope that this version of Mara had a connection with Luke Skywalker. Luke died at the end of The Last Jedi, and while it's possible Mark Hamill could reprise the role one more time as a Force Ghost, Mara could be a good way for us to learn more about Luke in the period between Return of the Jedi and The Force Awakens. However, if Episode IX does take major creative liberties with her, I worry she could end up being part of the Knights of Ren.