In a video commentary, on the Official Star Wars website, supervising director Dave Filoni explains how Darth Revan was supposed to appear in the episode of Clone Wars that was aired last week: “Ghosts of Morits”:
We designed them. They are in The Clone Wars style. We modeled them in The Clone Wars style, and we shot the scene in the episode. The scene exists. But it never made it into animation, it only existed in layout. I was very apprehensive of this scene, as cool as it was, because the implication of it. Which is that, these Sith Lords could separate themselves from the Force, and somehow talk to the Son.
George watches it, and he loved it, it was great. But eventually, I got a call from George. And he said, you know, I’ve been really thinking about this, and we should really take that scene out, with the Sith Lords.
Unfortunately it’s not possible to embed the video on this website, but you can wath the entire commentary here,