4. Star Wars: The New Jedi Order
Throughout the entirety of the now Legends material, there have been many sub-series that have taken the franchise in new and even unexpected directions. Legacy of the Force and Fate of the Jedi not only brought in fantastic story arcs featuring moments such as the fall of Jacen Solo and the death of beloved character Mara Jade Skywalker, but The New Jedi Order is a particular favorite.
Fans had been wondering for a long time about whether or not a brand new villain would be introduced. Not just a new villain though, but one unconnected to any previous characters. The door was then left open for the Yuuzhan Vong to invade the galaxy, and they did so in spades. Coming from outside of the galaxy we have come to know and love over many years, the Vong quickly and with a tenacity unlike anything seen before conquered many planets, including Coruscant, that our heroes were left in a state of disbelief.
What was impressive about them from their first appearance was their ability to live outside of the known boundaries of what we understood of the Force. Simply put, there was no way that the Vong could be sensed through the Force and were for the most part unaffected by the powers used on them.
As it stands in the current canon, there would be no way to introduce the Vong during the same period they were previously introduced in the old canon. They are, however, such good villains. It could be a good avenue to go down if Disney wanted to create a new trilogy of films — in the same way Grand Admiral Thrawn was reintroduced into canon through Rebels, perhaps as a way of continuing the stories of the characters presented during the sequel trilogy.