I talked to Principal Lead Systems Designer Damion Schubert, and he said that we'd definitely love to get more Sith corruption options in, but there are some challenges. First, we'd like to allow players to choose from different kinds of corruption, but it will require some work to get new options in. Second, there currently isn't any feature that mirrors this on the light side, which we'd also want to address in some way. This isn't something we'll be seeing in the near future, but it's something we would like to see in the game as well.
Tricky, tricky... how do depict another level opposite corruption... Maybe it can be as simple as adding and very faint but intermittent glow from the characters face? Something that could be seen in a close up, but not intrusive enough to confuse it with a buff.