Obsidian has said in interviews that it would be much darker than KOTOR 1. My idea which probably won't happen because it will be unsatisfying is that the Republic falls to the Sith whether you're dark or light. If you're dark, the final cutscene is of you on the bridge of your flagship unleashing some planetary bombardment upon Coruscant. If you're light, you're somehow deceived into thinking you cornered MSG on a remote world. Upon killing him, you find that it was Darth Sion behind the mask, even though you thought you killed him earlier (he already should be dead so it's got to be pretty hard to make sure you've killed him). When you leave the Sith temple, you find your ship destroyed, leaving you stranded. Cut to MSG conquering Coruscant. In KOTOR 3, your character (someone new) leads a rebellion against the Sith, similar to the situation in the Original Trilogy. Maybe you come across some people from KOTOR 2 on that remote world. That's probably not going to happen though. I don't think Lucasarts would let the Republic fall for the light side as well. Although, I do remember a line from the movies saying that the Republic has stood for a thousand years. Not four thousand or more. IIRC it was just a thousand. Perhaps this isn't the same Old Republic as in the prequel trilogy. Perhaps there was a time of Sith rule in between KOTOR trilogy and then.