So, to those who haven't kept up with Rebels. (I don't entirely blame you.) You may have missed the flood of KOTOR references and easter eggs flung into the episodes of late.
- Mandalore the Ultimate during Admiral Thrawns art scene.
- KOTOR ships and vehicles making their way into Rebel hands.
- Sith Holocrons, and the Sith Temple on Malachor.
In the final episode of Season 2 the gang makes their way to the Sith Temple on Malachor in search for knowledge to help against the Sith and all that nonsense. This is where Vader and Ashoka have their duel, and where the final inquisitors get killed off.
It's also where Ezra stumbles upon the Sith Holocron, and a supposed Sith super weapon that was possibly on par with the Death Star. When coming close to these a voice spoke, a female Sith Lord speaking to Ezra asking if he wanted to use this super weapon that would wipe out a majority of life in the galaxy.
The voice actress for this Sith Lord was the same actress as Asaj Ventress, however after an interview with Dave Filoni he came out to say it is not ventress and is indeed an ancient sith lord, whose name he is not allowed to speak of yet.
In the season 3 trailer for rebels you get to see a ghostly spirit, with the same voice actress of this Sith Lord, and for a small second you can see her face. She has an old wrinkly face with two long braids that fall down her shoulders, she looks IDENTICAL to Darth Traya.
Why do I think it is Traya? Well for starters, can you name me any other ancient female Sith Lords with a major presence on Malachor? Not to mention, the spew of KOTOR easter eggs and references.
AND Dave Filoni himself stating he was a fan of the KOTOR timeline, as well as having plans for Revan and Darth Bane cameos in the clonewars episode Shadow of Mortis, even having their models and the scene filmed, before scrapping the idea.
I think this also supports the rumors that Filoni is working on a Revan animated series to bring KOTOR into new canon.