Most Star Wars fans think Disney's purchase of Lucasfilm was ultimately a good thing, but there were some perceivable downsides. For one, all of the old expanded universe content was kind of thrown out the window since the official Star Wars canon was reset with the rest of those old beloved novels, comics and games now referred to as "legends." That said, Disney has been making use of the old canon and bringing it into the new fold, and they may have just done so in a pretty big way on the most recent episode of Star Wars Rebels. It now seems like Knights of the Old Republic, at least partially, is canon.
Warning, there will be minor spoilers ahead for the Star Wars Rebels episode "Trials of the Darksaber." As pointed out by Comicbook.com, during the episode, Kanan references the Mandalorian Wars that took place during the time of the Old Galactic Republic. Those who played the Star Wars: Knights of the Old Republic video games know that this was something heavily referenced in that era of Star Wars lore. Given the shoutout on Star Wars Rebels, it leads us to believe that, at least partially, Disney and Lucasfilm are officially acknowledging that time period as part of the new canon, which is a big deal. For those who may not be familiar, here is some background on the Mandalorian Wars from Wookieepedia.
"The Mandalorians raided star systems in the Outer Rim Territories for over a decade before they actually came into conflict with the Republic Military in 3965 BBY. Led by Mandalore the Ultimate, who pioneered the Neo-Crusader movement with the help of his lieutenant, Cassus Fett, the Mandalorians conquered systems along the eastern edge of the galaxy. Though their conquests included the near-extinction of the Cathar species, it was not until their assaults on worlds near the planet Taris that they drew the Republic's attention. After a year of small conflicts known as the False War, the Mandalorians broke through the Republic's lines and besieged Taris in 3963 BBY, and then invaded the Republic through three separate corridors in what became known as the Onslaught. The tide ultimately turned when a group of interventionist Jedi known as the Revanchists, led by the charismatic Revan and his friend Malak, joined the Republic Military in combating the Mandalorians. A tactical genius, Revan won several victories against the Mandalorians and began to reclaim lost territory, prompting Supreme Chancellor Tol Cressa to appoint him Supreme Commander in 3962 BBY. Driving back the Mandalorians, Revan forced a final showdown with Mandalore the Ultimate at the Battle of Malachor V in 3960 BBY. Revan personally defeated Mandalore in single combat as the Republic and Mandalorian fleets battled above Malachor V, and the activation of the superweapon known as the Mass Shadow Generator devastated both the planet and the participating fleets."
The Mandalorian Wars are, in themselves, significant to Star Wars history, but it is the name Revan that may stand out the most to hardcore fans here. Revan was a Jedi who found his way to the Dark Side and became known as Darth Revan, but never really firmly stood one way or the other. He is what is referred to as a "Grey Jedi." He is a very significant character to fans of the old Star Wars canon and one that many hoped would be included in the new canon. Since the Mandalorian Wars were referenced on the most recent episode of Star Wars Rebels, it seems like a safe bet to assume he was bundled in with that reference.
Star Wars Rebels is not only part of the new canon, but it has been made clear that this is not just some animated show taking place on the side of other, more important things. There were a ton of references to the show in Rouge One: A Star Wars Story, which helped to cement the importance of the show and firmly tie the series into the movies, meaning that things that happen on the show do affect the larger, Star Wars universe. Star Wars Rebels has also rescued other beloved elements from the Legends canon, such as bringing Grand Admiral Thrawn into the fold this season.
The events of Knights of the Old Republic are very far removed from the Star Wars timeline that any of the movies deal with, so it wouldn't necessarily mess anything up for Disney and Lucasfilm to acknowledge it as canon, while maybe making some tweaks, which they probably will. We'll have to wait and see how Lucasfilm approaches this in future episodes of Star Wars Rebels, or in comics, novels or even a new Knights of the Old Republic video game, which is something fans would surely love. For now, it seems like a safe bet that one of the most beloved parts of Star Wars history is safe from obscurity.