The Star Wars Universe's replacement for the evil Sith Lords were so vicious and violent, they will most likely never be seen on film. The franchise, while home to hundreds of different alien species, has a design language of sorts; a Star Wars alien will easily be identifiable by fans as belonging within the universe as opposed to, say, a Star Trek alien. But the most vicious of alien races did not fit this language (by design): the dreaded Yuuzhang Vong.
The Star Wars Expanded Universe has a history just as rich as that of the films, perhaps more so. The novel Splinter of the Mind's Eye is regarded as the first EU material; a novel written by Alan Dean Foster, it was quickly rendered non-canonical when George Lucas realized his franchise was phenomenally successful. After the release of Return of the Jedi, the franchise's popularity ebbed; no films were made for over a decade. 1999's The New Jedi Order series of books brought to the forefront an astounding new enemy in the form of the Yuuzhang Vong.
The Yuuzhang Vong originate from outside the Star Wars galaxy, and neither appear nor behave like any other creatures within. They are fanatically religious and technophobic to an absurd degree; indeed, their technology has a rather organic quality - they even fly in living spaceships, crafted by bio-engineers to fly through the stars to aid them in the galactic conquest. Most alarmingly, they are completely immune to the Force and cannot be detected or influenced using Force powers (the entire species maintained a symbiosis with their home planet that was severed in the wake of a massive war, causing the immunity).
The Yuuzhang Vong ritualistically scar themselves and embrace pain itself. They bio-implants are an important ritual in their culture, and they appear to many as vicious warriors who seemingly only exist to conquer and kill in the name of their Gods. For these and many other reasons, it's highly unlikely that Disney would ever allow the species to appear on screen. Religious fervor is a topic rarely addressed in the Star Wars films proper (outside of the Force being called a religion, which does not appear to have a creator deity; the practice is more akin to Buddhism and Shinto than any Abrahamic religion).
The Yuuzhang Vong have appeared in comics and books, but never on screen - though they were updated to canon status in the form of the Grysks, a very similar species. Bio-technology is so vastly different from the Star Wars aesthetic that many casual fans would most likely instantly reject the sight. The Yuuzhang Vong may never appear in a Star Wars film, but within the comics and other expanded universe material, they still continue their quest to destroy technology and replace it with their own twisted version.